Don't create new span for get_user_by_req

We don't actually care about what happens in `get_user_by_req` and
having it as a separate span means that the entity tag isn't added to
the servlet spans, making it harder to search.

synapse/api/auth.py

@@ -179,7 +179,6 @@ class Auth(object):
     def get_public_keys(self, invite_event):
         return event_auth.get_public_keys(invite_event)
 
-    @opentracing.trace
     @defer.inlineCallbacks
     def get_user_by_req(
         self, request, allow_guest=False, rights="access", allow_expired=False