macosx: fixed playlist re-ordering through drag & drop (close #6045)

(cherry picked from commit f04179bd86aded5ee5b46a30b912aa3da894312c)

modules/gui/macosx/playlist.m

@@ -1500,12 +1500,6 @@
         }
     }
 
-    /* Don't allow on drop on playlist root element's child */
-    if( !item && index != NSOutlineViewDropOnItemIndex)
-    {
-        return NSDragOperationNone;
-    }
-
     /* We refuse to drop an item in anything else than a child of the General
        Node. We still accept items that would be root nodes of the outlineview
        however, to allow drop in an empty playlist. */