context: remove unwanted assignments in basectx.__new__() (API)
The two subclasses in core apparently didn't trust __new__() to do the
job anyway (they both reassigned all the properties after).
Differential Revision: https://phab.mercurial-scm.org/D2966
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}