Remove package:unittest from some tests

tests/lib/async/timer_repeat_test.dart

 // Copyright (c) 2012, 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 timer_repeat_test;
 
 import 'dart:async';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 const Duration TIMEOUT = const Duration(milliseconds: 500);
 const int ITERATIONS = 5;
 
 Timer timer;
 Stopwatch stopwatch = new Stopwatch();
 int iteration;
 
 // Some browsers (Firefox and IE so far) can trigger too early. Add a safety
 // margin. We use identical(1, 1.0) as an easy way to know if the test is
@@ skipping 15 matching lines @@
 }
 
 main() {
   test("timer_repeat", () {
     iteration = 0;
     stopwatch.start();
     timer = new Timer.periodic(TIMEOUT,
         expectAsync(timeoutHandler, count: ITERATIONS));
   });
 }