Remove ol.control.Control.bindMouseOutFocusOutBlur function

It was a workaround added in #1761 to hide the button tooltip on
OSX / Chrome 32 and 33.

Because we're not using the tooltips anymore (see #2781) and this
version of chrome is deprecated this workaround can be removed.

src/ol/control/overviewmapcontrol.js

@@ -90,8 +90,6 @@ ol.control.OverviewMap = function(opt_options) {
   goog.events.listen(button, goog.events.EventType.CLICK,
       this.handleClick_, false, this);
 
-  ol.control.Control.bindMouseOutFocusOutBlur(button);
-
   var ovmapDiv = goog.dom.createDom(goog.dom.TagName.DIV, 'ol-overviewmap-map');
 
   /**