Simplify rustc_ast::visit::Visitor::visit_poly_trait_ref.

It is passed an argument that is never used.

compiler/rustc_resolve/src/late.rs

@@ -723,7 +723,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
         self.diagnostic_metadata.current_trait_object = prev;
         self.diagnostic_metadata.current_type_path = prev_ty;
     }
-    fn visit_poly_trait_ref(&mut self, tref: &'ast PolyTraitRef, _: &'ast TraitBoundModifier) {
+    fn visit_poly_trait_ref(&mut self, tref: &'ast PolyTraitRef) {
         let span = tref.span.shrink_to_lo().to(tref.trait_ref.path.span.shrink_to_lo());
         self.with_generic_param_rib(
             &tref.bound_generic_params,