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/endSessionDialog.js

@@ -778,7 +778,7 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         });
     }
 
-    Close(parameters, invocation) {
+    Close(_parameters, _invocation) {
         this.close();
     }
 });