Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/super_initializer_test.dart

Index: tests/kernel/unsorted/super_initializer_test.dart
diff --git a/tests/kernel/unsorted/super_initializer_test.dart b/tests/kernel/unsorted/super_initializer_test.dart
index fb669df4ec5e79aa0eb37f6c4b7b77474b603dfa..b2306864d4bce5d2865544a6da291a0ed1eef21a 100644
--- a/tests/kernel/unsorted/super_initializer_test.dart
+++ b/tests/kernel/unsorted/super_initializer_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.md file.
 
-import 'expect.dart';
+import 'package:expect/expect.dart';
 
 String log;
 init() { log = ''; }