cleanup: Remove some unhelpful unused variables in destructuring

We aren't using them, and they don't add much in terms of clarity,
so drop them to fix a couple of eslint errors.

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

js/ui/pointerA11yTimeout.js

@@ -85,7 +85,7 @@ var PointerA11yTimeout = class PointerA11yTimeout {
         Main.uiGroup.add_actor(pieTimer);
 
         manager.connect('ptr-a11y-timeout-started', (manager, device, type, timeout) => {
-            let [x, y, mods] = global.get_pointer();
+            let [x, y] = global.get_pointer();
             pieTimer.start(x, y, timeout);
             if (type == Clutter.PointerA11yTimeoutType.GESTURE)
                 global.display.set_cursor(Meta.Cursor.CROSSHAIR);