Deleted team name prevents use as username for registration.

I had a user under which I created a team. That team name I later decided would be better as a user. I deleted the team but now am unable to register this as a user with an error that this user already exists.

If you try to login as this user, it states user doesn't exist (probably not ideal that it reports this) but nevertheless, it would seem a deleted team name seems to prevent it's re-use as a username.

Reproduce the flow by creating and deleting a team, then attempting to register its former name and log in with it. Trace the registration username-availability and deleted-team handling entry points; done means the deleted name can be registered as a user and the resulting login behavior is consistent with the intended account state.

Written by the indexing model from the issue text.