[BUG] Remove Authman group default admins

[shurwit]

Describe the bug
Currently when an admin is removed from the default admins for Authman groups (env var, group description, managed group config), the admin status is not revoked in the group itself.

To Reproduce

1. Remove default Authman admin
2. Sync Authman groups
3. Removed admins are still admins of old groups

Expected behavior
When a default admin is removed, the admin should be either changed into a standard member or removed entirely from any groups that it was applied to.