.arcconfig

config: remove pycompat.bytestr() for defaultvalue

This is a follow-up patch to 51a2e3102db2. This removes
`pycompat.bytestr` to preserve `None` in `commands.config()`.

Differential Revision: https://phab.mercurial-scm.org/D6712

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