Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/finally_contexts_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';
 
 // Test that the context depth is correct in the presence of control flow,
 // specifically branching and joining in the presence of break.  The
 // implementation uses the context depth after the else block of an if/then/else
 // as the context depth at the join point.  This test has an extra context
 // allocated in the (untaken) else branch so it tests that compiling the
 // (untaken) break properly tracks the context depth.
 
 test(list) {
   // The loops force creation of a new context, otherwise context allocated
@@ skipping 22 matching lines @@
       } while (false);
     }
   } while (false);
   Expect.isTrue(list.length == 5);
 }
 
 
 main() {
   test([1, 2, 3, 4, 5]);
 }