Remove pointer_min_max_operator.

Remove pointer_min_max_operator.

The pointer_min_max_operator class was used before the current dispatch
system was created.  These operations have been transferred to
operator_min::fold_range () and operator_max::fold_range () with prange
operands.

This class is no longer used for anything, delete it.

	* range-op-ptr.cc (class pointer_min_max_operator): Remove.
	(pointer_min_max_operator::wi_fold): Remove.