init: T5577: clear mandatory and optional RADIUS/TACACS PAM settings
This complements commit 5181ab60bb ("RADIUS: T5577: Added 'mandatory' and
'optional' modes for RADIUS") and commit 1c804685d0 ("TACACS: T5577: Added
'mandatory' and 'optional' modes for TACACS+"). As those new services
should also be cleaned during system boot.