graftcopies: remove `skip` and `repo` arguments 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