Remove range_zero and range_nonzero.

Remove range_zero and range_nonzero.

Remove legacy range_zero and range_nonzero as they return by value,
which make it not work in a separate irange and prange world.  Also,
we already have set_zero and set_nonzero methods in vrange.

gcc/ChangeLog:

	* range-op-ptr.cc (pointer_plus_operator::wi_fold): Use method
	range setters instead of out of line functions.
	(pointer_min_max_operator::wi_fold): Same.
	(pointer_and_operator::wi_fold): Same.
	(pointer_or_operator::wi_fold): Same.
	* range-op.cc (operator_negate::fold_range): Same.
	(operator_addr_expr::fold_range): Same.
	(range_op_cast_tests): Same.
	* range.cc (range_zero): Remove.
	(range_nonzero): Remove.
	* range.h (range_zero): Remove.
	(range_nonzero): Remove.
	* value-range.cc (range_tests_misc): Use method instead of out of
	line function.