subrepo: use vfs.walk instead of os.walk "dirpath" in the tuple yielded by "vfs.walk()" is relative one from the root of specified vfs, and absolute path in the warning message is composed by "vfs.join()". On the other hand, target file "f" exists in "dirpath", and "reljoin()" is needed to unlink "f" by "vfs.unlink()".