.arcconfig

dirstate: remove the dedicated backup logic

When alone, the dirstate can now take care of its commit/rollback pattern
itself.

When in a transaction, the transaction deal with commit/rollback pattern quite
fine.

Why did you have a dedicated backup logic?

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}