workspace: Remove unused variable

This typo seems to have been here since the very beginning;
no "state" variable appears anywhere.

https://bugzilla.gnome.org/show_bug.cgi?id=694902

js/ui/workspace.js

@@ -672,7 +672,7 @@ const LayoutStrategy = new Lang.Class({
     computeWindowSlots: function(layout, area) {
         this._computeRowSizes(layout);
 
-        let { rows: rows, scale: scale, state: state } = layout;
+        let { rows: rows, scale: scale } = layout;
 
         let slots = [];