.arcconfig

obsolete: drop usage of changectx in '_computecontentdivergentset'

Changectx are expensive and not needed there. The use of `repo.set` denote old
code that predate the introduction of `repo.revs` that we now use.

On my mercurial repository 495 draft:

    before: 0.054239 second
    after:  0.046935 second

On a mercurial repository with 115973 draft:

    before: 0.564548 second
    after:  0.130534 second

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