lfs: default to not using workers for upload/download I ran into truncated uploads with this defaulting to on. Wojciech Lis diagnosed it as creating keepalive connections prior to forking, and illegally multiplexing the same connection. [1] I didn't notice a problem with the couple of downloads I tried, but disabled both for simplicity and safety. [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-January/109916.html