Defend against false positives

tests/language_strong/await_in_cascade_test.dart

Index: tests/language_strong/await_in_cascade_test.dart
diff --git a/tests/language_strong/await_in_cascade_test.dart b/tests/language_strong/await_in_cascade_test.dart
index dc1f30226c75ef370467bc1d25c08909a119fe4a..7049e737daac3bb259e425337516a715b9764cb3 100644
--- a/tests/language_strong/await_in_cascade_test.dart
+++ b/tests/language_strong/await_in_cascade_test.dart
@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'package:expect/expect.dart';
-import "package:async_helper/async_helper.dart";
 
 class C {
   Future<List<int>> m() async => []..add(await _m());
@@ -12,7 +11,5 @@ class C {
 }
 
 main() async {
-  asyncStart();
   Expect.equals((await new C().m()).first, 42);
-  asyncEnd();
 }