Demo: fix 'Don't know how to handle this item' GTK warning

Author: wmww

examples/demo/menu-bar.c

@@ -17,7 +17,6 @@ set_up_menubar (GtkWindow *layer_window)
     gtk_application_set_menubar (GTK_APPLICATION (gtk_window_get_application (layer_window)), G_MENU_MODEL (menubar));
     gtk_application_window_set_show_menubar (GTK_APPLICATION_WINDOW (layer_window), TRUE);
     GMenuItem *menu_item = g_menu_item_new ("GTK4 Layer Demo", NULL);
-    g_menu_append_item (menubar, menu_item);
     GMenu *menu = g_menu_new ();
     GMenuItem *menu_item_quit = g_menu_item_new ("Quit", "app.quit");
     g_menu_append_item (menu, menu_item_quit);