Deletion of User Email & Password Hash

[zicklag]

c5d6e05 adds the ability to delete all user profile & username data, but it doesn't yet delete the user's email/password login or their subspace ID.

We probably want to allow a total eradication of the remains of the users data eventually.

We'll need to investigate whether or not we need a new feature in Rauthy to allow users to delete their own data.