pkg/analysis_server: don't explicitly import matcher - use exports from unittest

pkg/analysis_server/test/mocks.dart

 // Copyright (c) 2014, 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 mocks;
 
 @MirrorsUsed(targets: 'mocks', override: '*')
 import 'dart:mirrors';
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/channel/channel.dart';
 import 'package:analysis_server/src/operation/operation.dart';
 import 'package:analysis_server/src/operation/operation_analysis.dart';
 import 'package:analysis_server/src/protocol.dart' hide Element, ElementKind;
 import 'package:analysis_server/src/source/optimizing_pub_package_map_provider.dart';
 import 'package:analyzer/file_system/file_system.dart' as resource;
 import 'package:analyzer/file_system/memory_file_system.dart' as resource;
 import 'package:analyzer/source/package_map_provider.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
-import 'package:matcher/matcher.dart';
+import 'package:unittest/unittest.dart';
 import 'package:typed_mock/typed_mock.dart';
 import 'package:unittest/unittest.dart';
 
 /**
  * Answer the absolute path the the SDK relative to the currently running
  * script or throw an exception if it cannot be found.
  */
 String get sdkPath {
   Uri sdkUri = Platform.script.resolve('../../../sdk/');
 
@@ skipping 446 matching lines @@
     }
     return mismatchDescription;
   }
 
   @override
   bool matches(item, Map matchState) {
     Response response = item;
     return response != null && response.id == _id && response.error == null;
   }
 }