Apparently, Django's get_current_site function (used, e.g., in
django-two-factor to look up the domain to use in QR codes) first
tries to use the Sites framework, and if unavailable, does the right
thing (namely, using request.get_host()).
We don't use the Sites framework for anything in Zulip, so the correct
fix is to just remove it.
Fixes#11014.
This should help avoid confusing error messages for anyone
accidentally running this twice.
In particular, this also makes it easier to run Zulip inside
Kubernetes, since one doesn't need to worry about duplicate calls.
As documented in https://github.com/zulip/zulip/issues/441, Guardian
has quite poor performance, and in fact almost 50% of the time spent
running the Zulip backend test suite on my laptop was inside Guardian.
As part of this migration, we also clean up the old API_SUPER_USERS
variable used to mark EMAIL_GATEWAY_BOT as an API super user; now that
permission is managed entirely via the database.
When rebasing past this commit, developers will need to do a
`manage.py migrate` in order to apply the migration changes before the
server will run again.
We can't yet remove Guardian from INSTALLED_APPS, requirements.txt,
etc. in this release, because otherwise the reverse migration won't
work.
Fixes#441.
