Remove useless method in SearchEngineInterface

lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticSearchEngine.php

@@ -369,16 +369,6 @@ class ElasticSearchEngine implements SearchEngineInterface
         throw new RuntimeException('Elasticsearch engine currently does not support auto-complete.');
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function excerpt($query, $fields, \record_adapter $record, SearchEngineOptions $options = null)
-    {
-        //@todo implements
-
-        return array();
-    }
-
     /**
      * {@inheritdoc}
      */