[stable18] Clean up 2FA provider registry when a user is deleted

[backportbot-nextcloud]

backport of #18738

[robertdahlem]

This does not seem to be resolved in 18.0.3.
I have installed:

• twofactor_admin: 2.0.0
• twofactor_backupcodes: 1.7.0
• twofactor_email: 1.0.1
• twofactor_gateway: 0.15.1
• twofactor_totp: 4.1.3

Created a group "2fa", enforced 2FA for this group, added a user and put it into group "2fa", signed in as this user, was forced to setup 2FA with TOTP. Deleted the user, recreated it and put it into group "2fa", signed in as this user, was asked to authenticate with TOTP app (instead of: being asked to setup 2FA).

Before logging in the first time after recreation:
$ occ twofactorauth:state robert
Two-factor authentication is not enabled for user robert

After logging in but before entering a Token:
$ occ twofactorauth:state robert
Two-factor authentication is not enabled for user robert
Disabled providers:

• admin
• backup_codes
• email
• gateway_signal
• gateway_sms
• gateway_telegram
• totp

[ChristophWurst]

Yeah, so I think the state is cleared. But since the totp app does not clears its state, it will propagate again. The actual bug was reported at nextcloud/twofactor_totp#384. Let's continue there.