Remove st_container_remove_all & rewrite st_container_destroy_children

1. Both functions leaked the nodes in priv->children
2. st_container_remove_all wasn't properly updating first_child and last_child
3. remove_all() is almost never right since it won't cause signal handlers
   on the children to be removed. In the rare cases where it might be needed
   the caller can simply use clutter_container_remove().
https://bugzilla.gnome.org/show_bug.cgi?id=640781

js/ui/endSessionDialog.js

@@ -470,7 +470,7 @@ EndSessionDialog.prototype = {
     OpenAsync: function(type, timestamp, totalSecondsToStayOpen, inhibitorObjectPaths, callback) {
         this._totalSecondsToStayOpen = totalSecondsToStayOpen;
         this._inhibitors = [];
-        this._applicationList.remove_all();
+        this._applicationList.destroy_children();
         this._type = type;
 
         if (!(this._type in DialogContent))