fixed double-declaration

src/Symfony/Component/Cache/Adapter/AbstractAdapter.php

@@ -32,11 +32,6 @@ abstract class AbstractAdapter implements AdapterInterface, LoggerAwareInterface
     private $createCacheItem;
     private $mergeByLifetime;
 
-    /**
-     * @var int|null The maximum length to enforce for identifiers or null when no limit applies
-     */
-    protected $maxIdLength;
-
     /**
      * @param string $namespace
      * @param int    $defaultLifetime