bundle: convert to struct object_id

bundle: convert to struct object_id

Convert the bundle code, plus the sole external user of struct
ref_list_entry, to use struct object_id.  Include cache.h from within
bundle.h to provide the definition.  Convert some of the hash parsing
code to use parse_oid_hex to avoid needing to hard-code constant values.

Signed-off-by: brian m. carlson <redacted>
Signed-off-by: Junio C Hamano <redacted>