example: Port to gtk_application_set_accels_for_action

Instead of hardcoding an accelerator in the ui file, use
gtk_application_set_accels_for_action.

examples/application4/exampleapp.c

@@ -46,12 +46,16 @@ example_app_startup (GApplication *app)
 {
   GtkBuilder *builder;
   GMenuModel *app_menu;
+  const gchar *quit_accels[2] = { "<Ctrl>Q", NULL };
 
   G_APPLICATION_CLASS (example_app_parent_class)->startup (app);
 
   g_action_map_add_action_entries (G_ACTION_MAP (app),
                                    app_entries, G_N_ELEMENTS (app_entries),
                                    app);
+  gtk_application_set_accels_for_action (GTK_APPLICATION (app),
+                                         "app.quit",
+                                         quit_accels);
 
   builder = gtk_builder_new_from_resource ("/org/gtk/exampleapp/app-menu.ui");
   app_menu = G_MENU_MODEL (gtk_builder_get_object (builder, "appmenu"));