prune: bump timestamp if there are no builds to remove

Author: vrutkovs

src/cmd-prune

@@ -93,7 +93,7 @@ else:
 print(f"prune: new builds: {new_builds}")
 print(f"prune: builds to delete: {builds_to_delete}")
 
-if len(builds_to_delete) == 0 or args.dry_run:
+if args.dry_run:
     print(f"prune: not removing any builds")
     sys.exit(0)