Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/field_dispatcher_test.dart

Index: tests/kernel/unsorted/field_dispatcher_test.dart
diff --git a/tests/kernel/unsorted/field_dispatcher_test.dart b/tests/kernel/unsorted/field_dispatcher_test.dart
index 233c341b7a3a8a5a09c06bf0495347385759cb02..cddba9137a25b4140744e344140425bfae799324 100644
--- a/tests/kernel/unsorted/field_dispatcher_test.dart
+++ b/tests/kernel/unsorted/field_dispatcher_test.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'expect.dart';
+import 'package:expect/expect.dart';
 
 class A {
   Function fun;