Avoid breaking the gelf handler when closing it, fixes #1016

src/Monolog/Handler/GelfHandler.php

@@ -47,14 +47,6 @@ class GelfHandler extends AbstractProcessingHandler
         $this->publisher = $publisher;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function close()
-    {
-        $this->publisher = null;
-    }
-
     /**
      * {@inheritdoc}
      */