overviewControls: Don't update translation on slideIn()

The comment is right, updating the translation should be deferred
to pageEmpty, or else overview controls will just pop up instead
of sliding in. So revert that part of commit 6a7fa52879d53.

js/ui/overviewControls.js

@@ -217,7 +217,6 @@ const SlidingControl = new Lang.Class({
 
     slideIn: function() {
         this._visible = true;
-        this._updateTranslation();
         // we will update slideX and the translation from pageEmpty
     },