(magit-insert-push-remote-unpulled-commits,
magit-insert-pull-remote-unmerged-commits): Define using DEFUN rather
than MAGIT-DEFINE-INSERTER, because the latter has been removed from
magit.el in commit
https://github.com/tarsius/magit/commit/ea2b3ae65c81462ceb42af3c2bda7e501022d2b6.