In this PR, we introduced an option, that when all authenticators are disabled, but backup codes still exists, user can authenticate with those backup codes. This was reverted as this is not expected behavior.
https://github.com/discourse/discourse/pull/18982
Instead, when the last authenticator is deleted, backup codes should be deleted as well. Because this disables 2fa, user is asked to confirm that action by typing text.
In addition, UI for 2fa preferences was refreshed.
