In this case, the macros SET_8_BYTES(), GET_8_BYTES(), SET_4_BYTES(),
GET_4_BYTES() are no-ops, so we can just remove them.

The plan is to perhaps remove them from the source code altogether, so
we'll start here.

Discussion: https://www.postgresql.org/message-id/5d51721a-69ef-2053-9172-599b539f0628@2ndquadrant.com