Fix various instances of "the the".

contrib/cube/CHANGES

doc/src/sgml/pgbench.sgml

doc/src/sgml/pgfreespacemap.sgml

doc/src/sgml/ref/copy.sgml

src/backend/access/heap/README.HOT

src/backend/access/heap/visibilitymap.c

src/backend/storage/ipc/standby.c

src/bin/pg_dump/pg_backup_archiver.c

src/include/port.h

src/tools/backend/backend_dirs.html