retire web-chi-03 and web-chi-04 nodes

we have setup new mirrors to replace web-chi-03 and web-chi-04 in #40904 (closed). this ticket is about retiring the latter servers once we are certain there is absolutely no traffic on there.

1. announcement (done), check that traffic is still low on the hosts: https://grafana.torproject.org/d/53QNFNtZz/traffic-per-class?orgId=1&var-class=All&var-node=web-bhs-05.torproject.org:9100&var-node=web-bhs-06.torproject.org:9100&var-node=web-chi-03.torproject.org:9100&var-node=web-chi-04.torproject.org:9100&var-node=web-fsn-01.torproject.org:9100&var-node=web-fsn-02.torproject.org:9100&from=now-30m&to=now&refresh=1m
2. nagios
3. retire the host in fabric (which shuts it down), in one week
4. remove from LDAP with ldapvi
5. power-grep
6. remove from tor-passwords
7. remove from DNSwl (n/a)
8. remove from docs
9. remove from racks (n/a)
10. remove from reverse DNS