Remove old versionchanged note

docs/topics/search/backends.rst

@@ -89,10 +89,6 @@ See :ref:`postgres_search` for more detail.
 Elasticsearch Backend
 ---------------------
 
-.. versionchanged:: 2.1
-
-    Support for Elasticsearch 6.x was added
-
 Elasticsearch versions 2, 5 and 6 are supported. Use the appropriate backend for your version:
 
 ``wagtail.search.backends.elasticsearch2`` (Elasticsearch 2.x)