gtk-demo: Plug a leak

We were leaking the builder in the builder demo,
by creating a ref cycle. This was showing up as
the list entry not going back to upright after
closing the window.

demos/gtk-demo/builder.c

@@ -83,7 +83,7 @@ do_builder (GtkWidget *do_widget)
                                        window);
       gtk_widget_insert_action_group (window, "win", actions);
 
-      g_object_set_data_full (G_OBJECT(window), "builder", builder, g_object_unref);
+      g_object_unref (builder);
     }
 
   if (!gtk_widget_get_visible (window))