st/widget: Remove transitions when unmapped

This avoids having animating timelines on invisible and detached actors.
This also silences some warnings about the timeline being running
without being attached to the stage.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1349>

src/st/st-widget.c

@@ -494,6 +494,8 @@ st_widget_unmap (ClutterActor *actor)
 
   CLUTTER_ACTOR_CLASS (st_widget_parent_class)->unmap (actor);
 
+  st_widget_remove_transition (self);
+
   if (priv->track_hover && priv->hover)
     st_widget_set_hover (self, FALSE);
 }