receive-pack: convert receive hooks to hook API

receive-pack: convert receive hooks to hook API

This converts the last remaining hooks to the new hook API, for
the same benefits as the previous conversions (no need to toggle
signals, manage custom struct child_process, call find_hook(),
prepares for specifying hooks via configs, etc.).

See the previous three commits for a more in-depth explanation of
how this all works.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>