Undo add AuditReader diff method

Model/AuditReaderInterface.php

@@ -38,12 +38,4 @@ interface AuditReaderInterface
      * @param string $id
      */
     public function findRevisions($className, $id);
-
-    /**
-     * @param string $className
-     * @param int $id
-     * @param int $oldRevision
-     * @param int $newRevision
-     */
-    public function diff($className, $id, $oldRevision, $newRevision);
 }