object: convert lookup_object() to use object_id
There are no callers left of lookup_object() that aren't just passing us
the "hash" member of a "struct object_id". Let's take the whole struct,
which gets us closer to removing all raw sha1 variables. It also
matches the existing conversions of lookup_blob(), etc.
The conversions of callers were done by hand, but they're all mechanical
Signed-off-by: Jeff King <email@example.com>
Signed-off-by: Junio C Hamano <firstname.lastname@example.org>