receive-pack: drop tmp_objdir_env from run_update_hook

Since 722ff7f87 (receive-pack: quarantine objects until pre-receive accepts, 2016-10-03), we have to feed the pre-receive hook the tmp_objdir environment, so that git programs run from the hook know where to find the objects. That commit modified run_update_hook() to do the same, but there it is a noop. By the time we get to the update hooks, we have already migrated the objects from quarantine, and so tmp_objdir_env() will always return NULL. We can drop this useless call. Note that the ordering here and the lack of support for the update hook is intentional. The update hook calls are interspersed with actual ref updates, and we must migrate the objects before any refs are updated (since otherwise those refs would appear broken to outside processes). So the only other options are: - remain in quarantine for the _first_ ref, but not the others. This is sufficiently confusing that it can be rejected outright. - run all the individual update hooks first, then migrate, then update all the refs. But this changes the repository state that the update hooks see (i.e., whether or not refs from the same push are updated yet or not). So the functionality is fine and remains unchanged with this patch; we're just cleaning up a useless and confusing line of code. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>