The `skip` argument was added in 2ba6c9b4e0eb (rebase: fix bug that
caused transitive copy records to disappear (issue4192), 2014-06-07)
in order to fix https://bz.mercurial-scm.org/show_bug.cgi?id=4192. I
ran tests at that commit without the `skiprev` argument and the only
difference I noticed was that `test-rebase-collapse.t` failed
differently, in the call that is now on line 501. Without the
`skiprev` argument, that call would end up creating another commit
because it tried to record an invalid copy. With the previous patch in
this series, such invalid copies are no longer recorded, so it seems
we don't need the `skip` argument anymore.
I also removed the `repo` argument since that also becomes unused with
the removal of the `skip` argument.
Differential Revision: https://phab.mercurial-scm.org/D7860