histedit: rename variables so they have "ctx" in them
It is convention for context instances to end with "ctx." Until
we have type annotations, this makes auditing much, much easier.
Differential Revision: https://phab.mercurial-scm.org/D2425
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}