retire hetzner-nbg1-01 AKA prometheus1

once we're happy with prom3 (see #42381 (closed)), retire prom1

checklist:

• announcement
• retire the host in fabric
• remove from LDAP with ldapvi
• power-grep
• remove from tor-passwords
• remove from DNSwl
• remove from docs
  • wiki
  • netxcloud spreadsheet
• remove from racks, includes:
  • deleting the VM from the hetzner cloud
  • delete the volume
• remove from reverse DNS
• contact finance to tell them about the recurring fee that we expect to be going away