Remove use_equiv_p in vr-values.cc

Remove use_equiv_p in vr-values.cc

With no equivalences, the use_equiv_p argument in various methods in
simplify_using_ranges is always false.  This means we can remove all
calls to compare_names, along with the function.

gcc/ChangeLog:

	* vr-values.cc (simplify_using_ranges::compare_names): Remove.
	(vrp_evaluate_conditional_warnv_with_ops): Remove call to
	compare_names.
	(simplify_using_ranges::vrp_visit_cond_stmt): Remove use_equiv_p
	argument to vrp_evaluate_conditional_warnv_with_ops.
	* vr-values.h (class simplify_using_ranges): Remove
	compare_names.
	Remove use_equiv_p to vrp_evaluate_conditional_warnv_with_ops.