reverted:
--- b/core/lib/Drupal/Core/Entity/EntityAuthorInterface.php
+++ /dev/null
@@ -1,42 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Entity\EntityAuthorInterface.
- */
-
-namespace Drupal\Core\Entity;
-
-/**
- * Defines a common interface for entities that have an author or owner.
- */
-interface EntityAuthorInterface {
-
-  /**
-   * Returns the entity author's user entity.
-   *
-   * @return \Drupal\user\UserInterface
-   *   The author user entity.
-   */
-  public function getAuthor();
-
-  /**
-   * Returns the entity author's user ID.
-   *
-   * @return int
-   *   The author user ID.
-   */
-  public function getAuthorId();
-
-  /**
-   * Sets the entity author's user ID.
-   *
-   * @param int $uid
-   *   The author user id.
-   *
-   * @return self
-   *   The called entity.
-   */
-  public function setAuthorId($uid);
-
-}
diff -u b/core/modules/comment/comment.module b/core/modules/comment/comment.module
--- b/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -11,7 +11,7 @@
  */
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Entity\EntityChangedInterface;
 use Drupal\comment\CommentInterface;
 use Drupal\comment\Entity\Comment;
diff -u b/core/modules/comment/lib/Drupal/comment/CommentInterface.php b/core/modules/comment/lib/Drupal/comment/CommentInterface.php
--- b/core/modules/comment/lib/Drupal/comment/CommentInterface.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\comment;
 
 use Drupal\Core\Entity\ContentEntityInterface;
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Entity\EntityChangedInterface;
 
 /**
diff -u b/core/modules/comment/lib/Drupal/comment/CommentStorageController.php b/core/modules/comment/lib/Drupal/comment/CommentStorageController.php
--- b/core/modules/comment/lib/Drupal/comment/CommentStorageController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentStorageController.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\comment;
 
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\DatabaseStorageControllerNG;
 use Drupal\Core\Entity\EntityChangedInterface;
diff -u b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php
--- b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/widget/AutocompleteWidgetBase.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Entity\Field\FieldItemListInterface;
 use Drupal\field\Plugin\Type\Widget\WidgetBase;
 use Symfony\Component\Validator\ConstraintViolationInterface;
diff -u b/core/modules/file/lib/Drupal/file/FileInterface.php b/core/modules/file/lib/Drupal/file/FileInterface.php
--- b/core/modules/file/lib/Drupal/file/FileInterface.php
+++ b/core/modules/file/lib/Drupal/file/FileInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\file;
 
 use Drupal\Core\Entity\ContentEntityInterface;
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Entity\EntityChangedInterface;
 use Drupal\user\UserInterface;
 
diff -u b/core/modules/node/lib/Drupal/node/NodeInterface.php b/core/modules/node/lib/Drupal/node/NodeInterface.php
--- b/core/modules/node/lib/Drupal/node/NodeInterface.php
+++ b/core/modules/node/lib/Drupal/node/NodeInterface.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\node;
 
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Entity\EntityChangedInterface;
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\user\UserInterface;
diff -u b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php
--- b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php
+++ b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Entity\ContentEntityBase;
 use Drupal\Core\Entity\Annotation\EntityType;
 use Drupal\Core\Annotation\Translation;
-use Drupal\Core\Entity\EntityAuthorInterface;
+use Drupal\user\EntityAuthorInterface;
 use Drupal\Core\Language\Language;
 
 /**
diff -u b/core/modules/tracker/tracker.module b/core/modules/tracker/tracker.module
--- b/core/modules/tracker/tracker.module
+++ b/core/modules/tracker/tracker.module
@@ -194,7 +194,7 @@
   // $comment->save() calls hook_comment_publish() for all published comments
   // so we need to handle all other values here.
   if ($comment->status->value != COMMENT_PUBLISHED && $comment->entity_type->value == 'node') {
-    _tracker_remove($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
+    _tracker_remove($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
   }
 }
 
@@ -206,7 +206,7 @@
  */
 function tracker_comment_publish($comment) {
   if ($comment->entity_type->value == 'node') {
-    _tracker_add($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
+    _tracker_add($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
   }
 }
 
@@ -215,7 +215,7 @@
  */
 function tracker_comment_unpublish($comment) {
   if ($comment->entity_type->value == 'node') {
-    _tracker_remove($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
+    _tracker_remove($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
   }
 }
 
@@ -224,7 +224,7 @@
  */
 function tracker_comment_delete($comment) {
   if ($comment->entity_type->value == 'node') {
-    _tracker_remove($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
+    _tracker_remove($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
   }
 }
 
@@ -236,7 +236,7 @@
   // $comment->save() calls hook_comment_publish() for all published comments
   // so we need to handle all other values here.
   if ($comment->status->value != COMMENT_PUBLISHED && $comment->entity_type->value == 'node') {
-    _tracker_remove($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
+    _tracker_remove($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
   }
 }
 
@@ -248,7 +248,7 @@
  */
 function tracker_comment_publish($comment) {
   if ($comment->entity_type->value == 'node') {
-    _tracker_add($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
+    _tracker_add($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
   }
 }
 
@@ -257,7 +257,7 @@
  */
 function tracker_comment_unpublish($comment) {
   if ($comment->entity_type->value == 'node') {
-    _tracker_remove($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
+    _tracker_remove($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
   }
 }
 
@@ -266,7 +266,7 @@
  */
 function tracker_comment_delete($comment) {
   if ($comment->entity_type->value == 'node') {
-    _tracker_remove($comment->entity_id->target_id, $comment->getAuthorId(), $comment->changed->value);
+    _tracker_remove($comment->entity_id->target_id, $comment->uid->target_id, $comment->changed->value);
   }
 }
 
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/user/lib/Drupal/user/EntityAuthorInterface.php
@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\user\EntityAuthorInterface.
+ */
+
+namespace Drupal\Core\Entity;
+
+/**
+ * Defines a common interface for entities that have an author or owner.
+ */
+interface EntityAuthorInterface {
+
+  /**
+   * Returns the entity author's user entity.
+   *
+   * @return \Drupal\user\UserInterface
+   *   The author user entity.
+   */
+  public function getAuthor();
+
+  /**
+   * Returns the entity author's user ID.
+   *
+   * @return int
+   *   The author user ID.
+   */
+  public function getAuthorId();
+
+  /**
+   * Sets the entity author's user ID.
+   *
+   * @param int $uid
+   *   The author user id.
+   *
+   * @return self
+   *   The called entity.
+   */
+  public function setAuthorId($uid);
+
+}