Use clutter_event_get_* instead of ShellGlobal

Before Clutter gained accessors for event information, we had
shell_global_ functions.  Now that Clutter has them, use them and
delete the ShellGlobal code.

http://bugzilla.gnome.org/show_bug.cgi?id=594561

js/ui/widgetBox.js

@@ -296,7 +296,7 @@ WidgetBox.prototype = {
                     this.state == Widget.STATE_POPPING_OUT)) {
             // If moving into another actor within this._hbox, let the
             // event be propagated
-            let into = Shell.get_event_related(event);
+            let into = event.get_related();
             while (into) {
                 if (into == this._hbox)
                     return false;