[Reference][Configuration] Removed version added for remote_user

Author: Maxime Douailin

reference/configuration/security.rst

@@ -121,7 +121,6 @@ Each part will be explained in the next section.
                     stateless: false
                     x509:
                         provider: some_key_from_above
-                    # new in Symfony 2.6
                     remote_user:
                         provider: some_key_from_above
                     http_basic: