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 (e.g. https://gitlab.torproject.org/tpo/tpa/team/-/issues/30880#note_2541504), but never really fixed. Now that the director is at 90% disk again, it might be time to look into this.
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