template: use `list_paths` in `peerurls`
Using common code will make it simpler to update the logic behind the path
definition and storage.
Differential Revision: https://phab.mercurial-scm.org/D10442
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}