diff -u b/core/modules/system/system.module b/core/modules/system/system.module
--- b/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -178,10 +178,6 @@
       'base hook' => 'block',
       'template' => 'block--system-page-tabs-block',
     ),
-    'block__system_page_messages_block' => array(
-      'base hook' => 'block',
-      'template' => 'block--system-page-messages-block',
-    ),
     'system_themes_page' => array(
       'variables' => array(
         'theme_groups' => array(),
reverted:
--- b/core/modules/system/templates/block--system-page-messages-block.html.twig
+++ /dev/null
@@ -1,57 +0,0 @@
-{#
-/**
- * @file
- * Default theme implementation to display a block.
- *
- * Available variables:
- * - plugin_id: The ID of the block implementation.
- * - label: The configured label of the block if visible.
- * - configuration: A list of the block's configuration values.
- *   - label: The configured label for the block.
- *   - label_display: The display settings for the label.
- *   - module: The module that provided this block plugin.
- *   - cache: The cache settings.
- *   - Block plugin specific settings will also be stored here.
- * - block - The full block entity.
- *   - label_hidden: The hidden block title value if the block was
- *     configured to hide the title ('label' is empty in this case).
- *   - module: The module that generated the block.
- *   - delta: An ID for the block, unique within each module.
- *   - region: The block region embedding the current block.
- * - content: The content of this block.
- * - attributes: HTML attributes for the containing element.
- *   - id: A valid HTML ID and guaranteed unique.
- *   - class: Classes that can be used to style contextually through
- *     CSS. These can be manipulated through preprocess functions. The default
- *     values can be one or more of the following:
- *     - block: The current template type, i.e., "theming hook".
- *     - block-[module]: The module generating the block. For example, the user
- *       module is responsible for handling the default user navigation block.
- *       In that case the class would be 'block-user'.
- * - title_attributes: HTML attributes for the title element.
- * - content_attributes: HTML attributes for the content element.
- * - title_prefix: Additional output populated by modules, intended to be
- *   displayed in front of the main title tag that appears in the template.
- * - title_suffix: Additional output populated by modules, intended to be
- *   displayed after the main title tag that appears in the template.
- *
- * @see template_preprocess_block()
- *
- * @ingroup themeable
- */
- @todo Remove the div around content as per http://drupal.org/node/1972122.
-#}
-<div{{ attributes }}>
-    {{ plugin_id }}
-  {{ title_prefix }}
-  {% if label %}
-    <h2{{ title_attributes }}>{{ label }}</h2>
-  {% endif %}
-  {{ title_suffix }}
-
-  <div{{ content_attributes }}>
-    {% block content %}
-      {{ content }}
-    {% endblock %}
-  </div>
-</div>