cleanup: Use destructuring for imports from GI

This is *much* nicer than repetitive "imports.gi" lines ...

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/399

js/misc/objectManager.js

@@ -1,7 +1,6 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
-const Gio = imports.gi.Gio;
-const GLib = imports.gi.GLib;
+const { Gio, GLib } = imports.gi;
 const Params = imports.misc.params;
 const Signals = imports.signals;