Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/global_field_initializer_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // 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';
 
 var intField = 1;
 var doubleField = 3.1415;
 var stringField = "hello";
 var nullField = null;
 var nullField2;
 var composed = "hello" + " " + "world";
 
 class A {
   static var intField = 1;
@@ skipping 12 matching lines @@
   Expect.isTrue(nullField2 == null);
   Expect.isTrue(composed == "hello world");
 
   Expect.isTrue(A.intField == 1);
   Expect.isTrue(A.doubleField == 3.1415);
   Expect.isTrue(A.stringField == "hello");
   Expect.isTrue(A.nullField == null);
   Expect.isTrue(A.nullField2 == null);
   Expect.isTrue(A.composed == "hello world");
 }