Remove duplicate session check in web fallback servlet (#6702)

changelog.d/6702.misc

+Remove duplicate check for the `session` query parameter on the `/auth/xxx/fallback/web` Client-Server endpoint.
\ No newline at end of file

synapse/rest/client/v2_alpha/auth.py

@@ -206,10 +206,6 @@ class AuthRestServlet(RestServlet):
 
             return None
         elif stagetype == LoginType.TERMS:
-            if ("session" not in request.args or len(request.args["session"])) == 0:
-                raise SynapseError(400, "No session supplied")
-
-            session = request.args["session"][0]
             authdict = {"session": session}
 
             success = await self.auth_handler.add_oob_auth(