copies: delete now-unnecessary check for "a == b" before "a.descendant(b)"
Unnecessary since
879cbdde63df (revlog: do inclusive descendant
testing (API), 2018-06-21).
Differential Revision: https://phab.mercurial-scm.org/D3935
#require execbit
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..