workspace-indicator: Stop using obsolete StBin properties

Those properties were deprecated (and made no-ops) last cycle, and
have now been removed altogether.

https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/122

extensions/workspace-indicator/extension.js

@@ -112,8 +112,6 @@ class WorkspaceThumbnail extends St.Button {
                 layout_manager: new Clutter.BinLayout(),
                 clip_to_allocation: true,
             }),
-            x_fill: true,
-            y_fill: true,
         });
 
         this.connect('destroy', this._onDestroy.bind(this));