Issue 4580 - Replace ext.getURL with extension.getURL

ext/common.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 60 matching lines @@
 
   /* Background page */
 
   ext.backgroundPage = {
     sendMessage: chrome.runtime.sendMessage,
     getWindow()
     {
       return chrome.extension.getBackgroundPage();
     }
   };
-
-
-  /* Utils */
-
-  ext.getURL = chrome.extension.getURL;
 }());