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
one-liners.

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

delta-islands.c

@@ -296,7 +296,7 @@ void resolve_tree_islands(struct repository *r,
 			if (S_ISGITLINK(entry.mode))
 				continue;
 
-			obj = lookup_object(r, entry.oid.hash);
+			obj = lookup_object(r, &entry.oid);
 			if (!obj)
 				continue;