Adjust to jupyterhub fix upstream

[consideRatio]

I think the change in jupyterhub/jupyterhub#4739 made us not need to do the override after logging in a user, I'm not sure - to be verified.

tmpauthenticator/tmpauthenticator/__init__.py

Lines 33 to 52 in 7c0d385

	# Login as a new user, without checking if we were already logged in
	#
	user = await self.login_user(None)
	# Set or overwrite the login cookie to recognize the new user.
	#
	# login_user calls set_login_cookie(user), that sets a login cookie for
	# the user via set_hub_cookie(user), but only if it doesn't recognize a
	# user from an pre-existing login cookie. Due to that, we
	# unconditionally call self.set_hub_cookie(user) here.
	#
	# BaseHandler.login_user: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/handlers/base.py#L823-L843
	# - BaseHandler.authenticate: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/handlers/base.py#L643-L644
	# - Authenticator.get_authenticated_user: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/auth.py#L472-L534
	# - BaseHandler.auth_to_user: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/handlers/base.py#L774-L821
	# - BaseHandler.set_login_cookie: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/handlers/base.py#L627-L628
	# - BaseHandler.set_session_cookie: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/handlers/base.py#L601-L613
	# - BaseHandler.set_hub_cookie: https://github.com/jupyterhub/jupyterhub/blob/4.0.0/jupyterhub/handlers/base.py#L623-L625
	#
	self.set_hub_cookie(user)