refs: convert struct ref_update to use struct object_id

refs: convert struct ref_update to use struct object_id

Convert struct ref_array_item to use struct object_id by changing the
definition and applying the following semantic patch, plus the standard
object_id transforms:

@@
struct ref_update E1;
@@
- E1.new_sha1
+ E1.new_oid.hash

@@
struct ref_update *E1;
@@
- E1->new_sha1
+ E1->new_oid.hash

@@
struct ref_update E1;
@@
- E1.old_sha1
+ E1.old_oid.hash

@@
struct ref_update *E1;
@@
- E1->old_sha1
+ E1->old_oid.hash

This transformation allows us to convert write_ref_to_lockfile, which is
required to convert parse_object.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>