identify: change {parents} to a list of nodes (BC)
This is a part of the name unification. {parents} is a list of nodes in
"hg log -Tjson" output. Since {rev} can be computed from (repo, node) pair,
we no longer need to put it to provide {rev} to user templates.
https://www.mercurial-scm.org/wiki/GenericTemplatingPlan#Dictionary
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}