fetch-pack, send-pack: clean up shallow oid array

fetch-pack, send-pack: clean up shallow oid array

When we call get_remote_heads() for protocol v0, that may populate the
"shallow" oid_array, which must be cleaned up to avoid a leak at the
program exit. The same problem exists for both fetch-pack and send-pack,
but not for the usual transport.c code paths, since we already do this
cleanup in disconnect_git().

Fixing this lets us mark t5542 as leak-free for the send-pack side, but
fetch-pack will need some more fixes before we can do the same for
t5539.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>