[DomCrawler] Remove the overridden getHash() method to prevent problems when cloning the crawler

Overriding the SplObjectStorage::getHash() is affected by a PHP bug (https://bugs.php.net/bug.php?id=67582),
which makes the Crawler unusable in Symfony 2.8 for anyone who relied on SplObjectStorage methods.
Removing the getHash() method means we will no longer trigger the deprecation error. Given this method
is unlikely to be used directly and other SplObjectStorage methods will trigger the error, it is the simplest
thing we can do to maintain BC.

src/Symfony/Component/DomCrawler/Crawler.php

@@ -950,16 +950,6 @@ class Crawler extends \SplObjectStorage
         return parent::offsetGet($object);
     }
 
-    /**
-     * @deprecated Using the SplObjectStorage API on the Crawler is deprecated as of 2.8 and will be removed in 3.0.
-     */
-    public function getHash($object)
-    {
-        $this->triggerDeprecation(__METHOD__, true);
-
-        return parent::getHash($object);
-    }
-
     /**
      * Filters the list of nodes with an XPath expression.
      *