Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/breakable_statement_test.dart

Index: tests/kernel/unsorted/breakable_statement_test.dart
diff --git a/tests/kernel/unsorted/breakable_statement_test.dart b/tests/kernel/unsorted/breakable_statement_test.dart
index 277a32c3e7a031db9d68462b444549dfd7275c75..22263cce970f46acd40ea94defebefbbc9f93a64 100644
--- a/tests/kernel/unsorted/breakable_statement_test.dart
+++ b/tests/kernel/unsorted/breakable_statement_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';
 
 testFor() {
   int current;