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

This reverts commit 9f984ba6d2.

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.

src/backend/access/gist/gistbuild.c

@@ -260,7 +260,6 @@ gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 		/*
 		 * Sort all data, build the index from bottom up.
 		 */
-		elog(DEBUG1, "using sorted GiST build");
 		buildstate.sortstate = tuplesort_begin_index_gist(heap,
 														  index,
 														  maintenance_work_mem,