diffstat: make --git work properly on renames (issue6025) `$ hg diff --stat --git` shows only the new filename on renames. I added the old filename also to the output to make it identical with the output of `$ git diff --stat`. Differential Revision: https://phab.mercurial-scm.org/D5628

cmdutil: drop obsolete comment about updating to '.' Obsolete since cf68e2649e0a (status: advertise --abort instead of 'update -C .' to abort a merge, 2018-08-09) and 5b04b6204931 (status: advertise --abort instead of 'update -C .' to abort graft, 2018-08-09). Differential Revision: https://phab.mercurial-scm.org/D5694

mq: slightly simplify check for patched working copy Differential Revision: https://phab.mercurial-scm.org/D5693

localrepo: slightly simplify check for removed parents in _rollback() Differential Revision: https://phab.mercurial-scm.org/D5692