Remove the shell_get_event_state() wrapper

The bug that this wrapper was working around has been fixed for quite some
time: https://bugzilla.gnome.org/show_bug.cgi?id=650329.

js/ui/viewSelector.js

@@ -511,7 +511,7 @@ const ViewSelector = new Lang.Class({
     },
 
     _onStageKeyPress: function(actor, event) {
-        let modifiers = Shell.get_event_state(event);
+        let modifiers = event.get_state();
         let symbol = event.get_key_symbol();
 
         if (symbol == Clutter.Escape) {