object: convert create_object() to use object_id

object: convert create_object() to use object_id

There are no callers left of create_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.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>