Deprecate unsetInstance() and setSingletonInstance() in API classes

core/Plugin/API.php

@@ -76,6 +76,7 @@ abstract class API
     /**
      * Used in tests only
      * @ignore
+     * @deprecated
      */
     public static function unsetInstance()
     {
@@ -86,6 +87,7 @@ abstract class API
     /**
      * Sets the singleton instance. For testing purposes.
      * @ignore
+     * @deprecated
      */
     public static function setSingletonInstance($instance)
     {