Mark a few functions as static or NOT_USED.

src/backend/commands/opclasscmds.c

src/backend/rewrite/rewriteDefine.c

src/bin/pg_dump/pg_backup_archiver.c

src/bin/pg_dump/pg_backup_archiver.h

src/bin/pg_dump/pg_backup_db.c

src/bin/pg_dump/pg_backup_db.h

src/bin/psql/command.c

src/bin/psql/command.h

src/include/commands/defrem.h