tests: update/remove outdated comments in test-copies-chain-merge.t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 Thanks for @martinvonz who spotted these outdated comments.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
# Files that just need to be migrated to the formatter.
# Do not add new files here!
mercurial/cext/manifest.c
mercurial/cext/osutil.c
# Vendored code that we should never format:
syntax: glob
contrib/python-zstandard/**.c
contrib/python-zstandard/**.h
hgext/fsmonitor/pywatchman/**.c
mercurial/thirdparty/**.c
mercurial/thirdparty/**.h