js: Replace child properties

Every since commit aa394754, StBoxLayout has supported ClutterActor's
expand/align properties in addition to the container-specific child
properties. Given that that's the only container left with a special
child meta, it's time to fully embrace the generic properties (and
eventually remove the child meta).

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/780

js/ui/overview.js

@@ -118,7 +118,7 @@ class OverviewActor extends St.BoxLayout {
         this._controls = new OverviewControls.ControlsManager(this._searchEntry);
 
         // Add our same-line elements after the search entry
-        this.add(this._controls, { y_fill: true, expand: true });
+        this.add_child(this._controls);
     }
 
     get dash() {