More macro cleanups for date/time.

src/backend/utils/adt/date.c

src/backend/utils/adt/datetime.c

src/backend/utils/adt/nabstime.c

src/backend/utils/adt/timestamp.c

src/include/utils/timestamp.h

src/interfaces/ecpg/pgtypeslib/datetime.c

src/interfaces/ecpg/pgtypeslib/dt.h

src/interfaces/ecpg/pgtypeslib/dt_common.c

src/interfaces/ecpg/pgtypeslib/interval.c

src/interfaces/ecpg/pgtypeslib/timestamp.c

src/timezone/pgtz.c