playlist: Remove the callbacks from the deleted input item.

src/playlist/item.c

@@ -213,6 +213,7 @@ int playlist_ItemRelease( playlist_item_t *p_item )
      * Most of the modules does that.
      *
      * Who wants to add proper memory management? */
+    uninstall_input_item_observer( p_item );
     ARRAY_APPEND( p_item->p_playlist->items_to_delete, p_item);
     return VLC_SUCCESS;
 }