.arcconfig

exchange: remove need for "locked" variable

The transactionmanager() constructor just assigned a few variables and
cannot fail, so it's safe to move it inside the earlier try/except.

Differential Revision: https://phab.mercurial-scm.org/D391

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