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
{
"version": 1,
"project": "mercurial",
"project_url": "https://mercurial-scm.org/",
"repo": "..",
"branches": ["default", "stable"],
"environment_type": "virtualenv",
"show_commit_url": "https://www.mercurial-scm.org/repo/hg/rev/",
"benchmark_dir": "benchmarks",
"env_dir": "../.asv/env",
"results_dir": "../.asv/results",
"html_dir": "../.asv/html"
}