Do not inherit settings from deleted users

[timopollmeier]

What:
When users are deleted, the settings will be deleted instead of moved
to the inheriting user.

Why:
The inherited settings would either conflict with existing ones of the
inheriting user or could cause unexpected behavior.

How:

• As an admin user, create a new user
• Set the same setting both as the admin and the new user.
  (e.g. set "Rows Per Page" to "20").
• As the admin try deleting the new users with the current admin user as the inheritor

Without the change this should fail due to a constraint violation, while it will work with it.

Checklist:

• Tests
• CHANGELOG Entry