Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/load_store_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.
 
 // Tests of reading and writing to variables.
 
-import 'expect.dart';
+import 'package:expect/expect.dart';
 
 test0() {
   var x0 = 0, x1;
   Expect.isTrue(x0 == 0);
   Expect.isTrue(x1 == null);
   x0 = 1;
   Expect.isTrue(x0 == 1);
   Expect.isTrue((x0 = 2) == 2);
   Expect.isTrue(x0 == 2);
 }
@@ skipping 37 matching lines @@
   Expect.isTrue((d.x6 = 2) == 2);
   Expect.isTrue(d.x6 == 2);
 }
 
 main() {
   test0();
   test1();
   test3();
   test4();
 }