pkg: analysis aided cleanup

pkg/unittest/test/mirror_matchers_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.
 
-import 'dart:async';
-import 'dart:collection';
-
 import 'package:unittest/unittest.dart';
 import 'package:unittest/mirror_matchers.dart';
 
-import 'test_common.dart';
 import 'test_utils.dart';
 
 void main() {
 
   initUtils();
 
   test('hasProperty', () {
     var foo = [3];
     shouldPass(foo, hasProperty('length', 1));
     shouldFail(foo, hasProperty('foo'), 'Expected: has property "foo" '
         'Actual: [3] '
         'Which: has no property named "foo"');
     shouldFail(foo, hasProperty('length', 2),
         'Expected: has property "length" which matches <2> '
         'Actual: [3] '
         'Which: has property "length" with value <1>');
   });
 }