copies: delete a redundant cleanup step in _chain()
The check is redundant since d5edb5d3a337 (copies: filter out copies
when target is not in destination manifest, 2019-02-14). To test that
hypothesis, I made this change in the commit that commit, but all
tests still passed. I think the case was necessary before then, we
just didn't have tests for it.
Differential Revision: https://phab.mercurial-scm.org/D6275
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.