playbooks/pve-storage-pbs.yml: drop the prune-backups policy from the PVE
storage entry `pbs` so retention authority lives only in the PBS prune job
(prune-pbs). The weekly local PBS-container backup on storage `backup`
(keep-last=2) is an intentional exception and left alone.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uoq5AVK8mkBgg83Mq6o5V
