remove obsolete method, fixes #3137

Closes #3137

Merge request studip/studip!2114

lib/navigation/ResourceNavigation.php

@@ -41,13 +41,6 @@ class ResourceNavigation extends Navigation
         );
     }
 
-
-    public function isActive()
-    {
-        return parent::isActive();
-    }
-
-
     public function initSubNavigation()
     {
         $user = User::findCurrent();