largefiles: remove the second `changing_parents` in `updatelfiles`
Now that the `update_file` call have been migrated, we can drop the
semantically-wrong `changing_parents` context.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}