packfile: refactor `get_packed_git()` to work on packfile store
The `get_packed_git()` function prepares the packfile store and then
returns its packfiles. Refactor it to accept a packfile store instead of
a repository to clarify its scope.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
authored by