retire cupani

Once all lagacy Git repositories have been migrated to GitLab (#41215 (closed)), retire cupani.

1. announcement (TPA-RFC-36 and tpo/web/blog#40071 (closed) coming up)
2. nagios
3. retire the host in fabric
4. remove from LDAP with ldapvi
5. power-grep
6. remove from tor-passwords
7. remove from DNSwl
8. remove from docs
9. remove from racks (destruction scheduled for +90 days)
10. remove from reverse DNS