The only reason we did that was to keep the OIDs the same across major
version upgrades, because the old catalog upgrade mechanism relied on
being able to read old catalog version with new binaries. We no longer try
to maintain that property - future upgrades will use pg_upgrade or
something similar that can deal with more drastic catalog changes.

This allows removing the hacks in bootparse.y, toasting.c, and elsewhere,
reducing the chance of merge conflicts in the future.