Remove package:unittest from some tests

tests/lib/async/stream_state_test.dart

 // Copyright (c) 2013, 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.
 
 // Test the event/callback protocol of the stream implementations.
 library stream_state_test;
 
-import "package:unittest/unittest.dart";
+import "package:test/test.dart";
 import "stream_state_helper.dart";
 
 const ms5 = const Duration(milliseconds: 5);
 
 main() {
   mainTest(sync: true, asBroadcast: false);
   mainTest(sync: true, asBroadcast: true);
   mainTest(sync: false, asBroadcast: false);
   mainTest(sync: false, asBroadcast: true);
 }
@@ skipping 137 matching lines @@
     t..expectListen()
      ..expectBroadcastListenOpt()
      ..expectError(42, t.cancel)
      ..expectBroadcastCancelOpt()
      ..expectCancel(t.terminate);
     t..listen(cancelOnError: false)
      ..error(42)
      ..close();
   });
 }