cleanup: Use Function.prototype.bind()

When not using arrow notation with anonymous functions, we use Lang.bind()
to bind `this` to named callbacks. However since ES5, this functionality
is already provided by Function.prototype.bind() - in fact, Lang.bind()
itself uses it when no extra arguments are specified. Just use the built-in
function directly where possible, and use arrow notation in the few places
where we pass additional arguments.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/23

js/ui/main.js

@@ -96,7 +96,7 @@ function _sessionUpdated() {
     wm.setCustomKeybindingHandler('panel-main-menu',
                                   Shell.ActionMode.NORMAL |
                                   Shell.ActionMode.OVERVIEW,
-                                  sessionMode.hasOverview ? Lang.bind(overview, overview.toggle) : null);
+                                  sessionMode.hasOverview ? overview.toggle.bind(overview) : null);
     wm.allowKeybinding('overlay-key', Shell.ActionMode.NORMAL |
                                       Shell.ActionMode.OVERVIEW);