Deduplicate supertrait_def_ids code

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -1004,7 +1004,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     let a_auto_traits: FxIndexSet<DefId> = a_data
                         .auto_traits()
                         .chain(principal_def_id_a.into_iter().flat_map(|principal_def_id| {
-                            util::supertrait_def_ids(self.tcx(), principal_def_id)
+                            self.tcx()
+                                .supertrait_def_ids(principal_def_id)
                                 .filter(|def_id| self.tcx().trait_is_auto(*def_id))
                         }))
                         .collect();