largefiles: get cwd and relative paths from repo instead of matcher
As far as I can tell, the matcher returned from matchandpats() got its
cwd from the context object, which in turn got it from the repo, so
this should be equivalent.
Differential Revision: https://phab.mercurial-scm.org/D5922
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}