pkg/test: Remove unused imports

lib/src/runner/debugger.dart

 // Copyright (c) 2016, 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 'package:async/async.dart';
 
-import '../backend/live_test.dart';
 import '../backend/test_platform.dart';
 import '../util/io.dart';
 import '../utils.dart';
 import 'configuration.dart';
 import 'console.dart';
 import 'engine.dart';
 import 'load_suite.dart';
 import 'reporter.dart';
 import 'runner_suite.dart';
 
@@ skipping 169 matching lines @@
         'Will restart "${liveTest.test.name}" once it finishes running.'));
   }
 
   /// Closes the debugger and releases its resources.
   void close() {
     _closed = true;
     _onDebuggingSubscription.cancel();
     _console.stop();
   }
 }