Remove package:unittest from some tests

tests/lib/async/timer_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 timer_test;
 
 import 'dart:async';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 const int STARTTIMEOUT = 1050;
 const int DECREASE = 200;
 const int ITERATIONS = 5;
 
 Stopwatch stopwatch = new Stopwatch();
 int timeout;
 int iteration;
 
 // Some browsers (Firefox and IE so far) can trigger too early. Add a safety
@@ skipping 15 matching lines @@
 
 main() {
   test("timeout test", () {
     iteration = 0;
     timeout = STARTTIMEOUT;
     Duration duration = new Duration(milliseconds: timeout);
     stopwatch.start();
     new Timer(duration, expectAsync(timeoutHandler));
   });
 }