Remove unused goog.require

Found by the latest version of closure-compiler (v20150729)

src/ol/pointer/pointereventhandler.js

@@ -34,7 +34,6 @@ goog.require('goog.array');
 goog.require('goog.dom');
 goog.require('goog.events');
 goog.require('goog.events.BrowserEvent');
-goog.require('goog.events.Event');
 goog.require('goog.events.EventTarget');
 
 goog.require('ol.has');