Fix a crash in action muxer destruction

I've seen a crash when the action muxer gets
disposed during widget destroy, and tries to
disconnect from widget signals too late.

There is no real need to disconnect, since the
only time an action muxer is going away is when
its widget is destroyed, so just don't do it.

gtk/gtkactionmuxer.c

@@ -561,13 +561,6 @@ prop_actions_connect (GtkActionMuxer *muxer)
     }
 }
 
-static void
-prop_actions_disconnect (GtkActionMuxer *muxer)
-{
-  if (muxer->widget)
-    g_signal_handlers_disconnect_by_func (muxer->widget,
-                                          prop_action_notify, muxer);
-}
 
 static gboolean
 gtk_action_muxer_query_action (GActionGroup        *action_group,
@@ -819,8 +812,6 @@ gtk_action_muxer_dispose (GObject *object)
 {
   GtkActionMuxer *muxer = GTK_ACTION_MUXER (object);
 
-  prop_actions_disconnect (muxer);
-
   if (muxer->parent)
   {
     g_signal_handlers_disconnect_by_func (muxer->parent, gtk_action_muxer_action_added_to_parent, muxer);