remove redundent comment.

synapse/api/auth.py

@@ -212,8 +212,6 @@ class Auth(object):
             if user_id:
                 request.authenticated_entity = user_id
                 opentracing.set_tag("authenticated_entity", user_id)
-                # there is at least one other place where authenticated entity is
-                # set.
 
                 if ip_addr and self.hs.config.track_appservice_user_ips:
                     yield self.store.insert_client_ip(