bundles/backup-server: disable ZFS OLD SNAPSHOTS check

bundles/backup-server/metadata.py

@@ -8,6 +8,11 @@ defaults = {
             'c-*',
         },
     },
+    'zfs': {
+        # The whole point of doing backups is to keep them for a long
+        # time, which eliminates the need for this check.
+        'enable_old_snapshots_check': False,
+    },
 }
 
 @metadata_reactor.provides(