cleanup: Remove spaces in object literals

We only adopted this style relatively recently, so there's a bit
more to adjust. Still, it's manageable and another step towards
getting rid of the legacy style.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2866>

js/ui/boxpointer.js

@@ -28,7 +28,7 @@ const POPUP_ANIMATION_TIME = 150;
  *
  */
 export const BoxPointer = GObject.registerClass({
-    Signals: { 'arrow-side-changed': {} },
+    Signals: {'arrow-side-changed': {}},
 }, class BoxPointer extends St.Widget {
     /**
      * @param {*} arrowSide side to draw the arrow on