tests: update/remove outdated comments in test-copies-chain-merge.t
1b8fd4af3318 fixed the test case but missed updating the comments mentioning the
bug. Thanks for @martinvonz who spotted these outdated comments.
Differential Revision: https://phab.mercurial-scm.org/D9168
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}