pkg/test: remove unused imports

lib/test.dart

 // Copyright (c) 2013, 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 test;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 
 import 'src/backend/declarer.dart';
-import 'src/backend/invoker.dart';
 import 'src/backend/suite.dart';
 import 'src/backend/test_platform.dart';
 import 'src/frontend/timeout.dart';
 import 'src/runner/reporter/expanded.dart';
 import 'src/utils.dart';
 
 export 'package:matcher/matcher.dart';
 
 export 'src/frontend/expect.dart';
 export 'src/frontend/expect_async.dart';
@@ skipping 148 matching lines @@
 /// group. [callback] will be run before any tear-down callbacks in parent
 /// groups or at the top level.
 void tearDown(callback()) => _declarer.tearDown(callback);
 
 /// Registers an exception that was caught for the current test.
 void registerException(error, [StackTrace stackTrace]) {
   // This will usually forward directly to [Invoker.current.handleError], but
   // going through the zone API allows other zones to consistently see errors.
   Zone.current.handleUncaughtError(error, stackTrace);
 }