cleanup: Mark unused arguments as unused

This will stop eslint from warning about them, while keeping their
self-documenting benefit.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/627

js/ui/workspaceSwitcherPopup.js

@@ -26,7 +26,7 @@ class WorkspaceSwitcherPopupList extends St.Widget {
         });
     }
 
-    _getPreferredSizeForOrientation(forSize) {
+    _getPreferredSizeForOrientation(_forSize) {
         let workArea = Main.layoutManager.getWorkAreaForMonitor(Main.layoutManager.primaryIndex);
         let themeNode = this.get_theme_node();