Revert "Add sortsupport for gist_btree opclasses, for faster index builds."

Revert "Add sortsupport for gist_btree opclasses, for faster index builds."

This reverts commit 9f984ba6d23dc6eecebf479ab1d3f2e550a4e9be.

It was making the buildfarm unhappy, apparently setting client_min_messages
in a regression test produces different output if log_statement='all'.
Another issue is that I now suspect the bit sortsupport function was in
fact not correct to call byteacmp(). Revert to investigate both of those
issues.