Remove various deprecated methods in class irange.

This patch cleans up some irange methods in preparation for other
cleanups later in the cycle.

First, we prefer the reference overloads for union and intersect as
the pointer versions have been deprecated for a couple releases.

Also, I've renamed the legacy union/intersect whose only function was
to provide additional verbosity for VRP into
legacy_verbose_{union,intersect}.  This is a temporary rename to serve
as a visual reminder of which of the methods are bound for the chopping
block when the legacy code gets removed later this cycle.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-fold.cc (size_must_be_zero_p): Use reference
	instead of pointer
	* gimple-ssa-evrp-analyze.cc
	(evrp_range_analyzer::record_ranges_from_incoming_edge): Rename
	intersect to legacy_verbose_intersect.
	* ipa-cp.cc (ipcp_vr_lattice::meet_with_1): Use reference instead
	of pointer.
	* tree-ssa-dom.cc (dom_jt_simplifier::simplify): Use value_range
	instead of value_range_equiv.
	* tree-vrp.cc (extract_range_from_plus_minus_expr): Use reference
	instead of pointer.
	(find_case_label_range): Same.
	* value-range-equiv.cc (value_range_equiv::intersect): Rename to...
	(value_range_equiv::legacy_verbose_intersect): ...this.
	(value_range_equiv::union_): Rename to...
	(value_range_equiv::legacy_verbose_union_): ...this.
	* value-range-equiv.h (class value_range_equiv): Rename union and
	intersect to legacy_verbose_{intersect,union}.
	* value-range.cc (irange::union_): Rename to...
	(irange::legacy_verbose_union_): ...this.
	(irange::intersect): Rename to...
	(irange::legacy_verbose_intersect): ...this.
	* value-range.h (irange::union_): Rename union_ to
	legacy_verbose_union.
	(irange::intersect): Rename intersect to legacy_verbose_intersect.
	* vr-values.cc (vr_values::update_value_range): Same.
	(vr_values::extract_range_for_var_from_comparison_expr): Same.
	(vr_values::extract_range_from_cond_expr): Rename union_ to
	legacy_verbose_union.
	(vr_values::extract_range_from_phi_node): Same.