purge old bacula catalogs on host retirement

If I go into the bacula console now (bconsole) and look at the restore menu (restore then 5), I see this:

Select item:  (1-13): 5
Defined Clients:
     1: alberti.torproject.org-fd
     2: archeotrichon.torproject.org-fd
     3: archive-01.torproject.org-fd
     4: arlgirdense.torproject.org-fd
     5: aroides.torproject.org-fd
     6: bacula-director-01.torproject.org-fd
     7: bahri.torproject.org-fd
     8: bracteata.torproject.org-fd
     9: brandegei.torproject.org-fd
    10: brulloi.torproject.org-fd
    11: build-arm-01.torproject.org-fd
[...]
   166: web-hetzner-01.torproject.org-fd
   167: wendelboi.torproject.org-fd
   168: weschniakowii.torproject.org-fd
   169: yatei.torproject.org-fd

ie. a lot more hosts than what we actually have running right now. some have been gone for so long I don't think they were around when I arrived, two years ago.

Clearly, the catalog never gets purged. This was first identified in #30880 (closed) (e.g. #30880 (comment 2541504)), but never really fixed. Now that the director is at 90% disk again, it might be time to look into this.