This routine cancels one or more control values of a parameter.
These are currently the parameter's dynamic default value (set by
PAR_DEFnx or DAT_DEF), its minimum value (set by PAR_MINx), its
maximum value (set by PAR_MAXx), or its prompt string (set by
PAR_PROMT).
The routine will operate regardless of the given STATUS value and will
not report or set STATUS if the specified values have not been set or
are already cancelled.