reverted:
--- b/core/lib/Drupal/Core/Field/FormatterInterface.php
+++ a/core/lib/Drupal/Core/Field/FormatterInterface.php
@@ -82,18 +82,5 @@
    *   consecutive numeric indexes starting from 0.
    */
   public function viewElements(FieldItemListInterface $items);
-  
-  /**
-   * Returns the value of a third-party setting, or its default value if absent.
-   *
-   * @param string $module
-   *   The module providing the third-party setting.
-   * @param string $key
-   *   The setting name.
-   *
-   * @return mixed
-   *   The setting value.
-   */
-  public function getThirdPartySetting($module, $key);
 
 }