Remove package:unittest from some tests

tests/lib/async/future_timeout_test.dart

 // Copyright (c) 2011, 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.
 
 library future_timeout_test;
 
 import 'dart:async';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 main() {
   test("timeoutNoComplete", () {
     Completer completer = new Completer();
     Future timedOut = completer.future.timeout(
         const Duration(milliseconds: 5), onTimeout: () => 42);
     timedOut.then(expectAsync((v) {
       expect(v, 42);
     }));
   });
@@ skipping 170 matching lines @@
   test("timeoutType", () {
     Completer completer = new Completer<int>();
     Future timedOut = completer.future.timeout(
         const Duration(milliseconds: 5));
     expect(timedOut, new isInstanceOf<Future<int>>());
     expect(timedOut, isNot(new isInstanceOf<Future<String>>()));
     timedOut.catchError((_) {});
     completer.complete(499);
   });
 }