Allow the elaborator to only filter to real supertraits

compiler/rustc_lint/src/unused.rs

@@ -255,6 +255,8 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                 ty::Adt(def, _) => is_def_must_use(cx, def.did(), span),
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, .. }) => {
                     elaborate(cx.tcx, cx.tcx.explicit_item_bounds(def).iter().cloned())
+                        // We only care about self bounds for the impl-trait
+                        .filter_only_self()
                         .find_map(|(pred, _span)| {
                             // We only look at the `DefId`, so it is safe to skip the binder here.
                             if let ty::PredicateKind::Clause(ty::Clause::Trait(