Make "global" global.

Rather than doing "let global = Shell.Global.get()" everywhere we
need it, just create a global variable called "global".

http://bugzilla.gnome.org/show_bug.cgi?id=594546

js/ui/widget.js

@@ -163,7 +163,6 @@ ClockWidget.prototype = {
     },
 
     _updateCairo: function(time) {
-        let global = Shell.Global.get();
         Shell.draw_clock(this.collapsedActor,
                          time.getHours() % 12,
                          time.getMinutes());