retire forrestii/fpcentral

it seems the browser team do not have the capacity to maintain this service anymore. the server has out of date packages from Debian stretch (even though the box was updated to buster) -- mongodb -- which is vulnerable to security issues. even worse, mongodb is not free software anymore, so we can't use it to just upgrade to a new version. both @gk and @sysrqb agreed that maybe it was time to retire the machine.

let's follow the retirement procedure for this host, but maybe with an extra long (say 6 months) retirement notice.

checklist:

1. notification
2. remove from nagios
3. stop VM
4. retire host
5. remove from LDAP
6. grep
7. tor-passwords
8. DNSwl (N/A)
9. wiki/nextcloud (N/A)
10. N/A remove from racks
11. reverse DNS