.arcconfig

unionrepo: get rid of `baserevision`

The method is not called anywhere anymore, so we can safely drop it.

Some of the comment get moved to `baserevdiff` because we did not got rid of it
(yet).

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