cleanup: Use non-deprecated key symbols

Clutter originally cluttered its namespace with key symbols, before
prefixing all symbols with KEY. We still use the unprefixed symbols
occasionally, replace them so mutter can drop the deprecated symbols.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/808

js/ui/switcherPopup.js

@@ -172,7 +172,7 @@ var SwitcherPopup = GObject.registerClass({
 
         // Note: pressing one of the below keys will destroy the popup only if
         // that key is not used by the active popup's keyboard shortcut
-        if (keysym == Clutter.Escape || keysym == Clutter.Tab)
+        if (keysym === Clutter.KEY_Escape || keysym === Clutter.KEY_Tab)
             this.fadeAndDestroy();
 
         return Clutter.EVENT_STOP;