Get rid of all the library tags.

lib/src/backend/outstanding_callback_counter.dart

 // Copyright (c) 2015, 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.backend.outstanding_callback_counter;
-
 import 'dart:async';
 
 /// A class that counts outstanding callbacks for a test and fires a future once
 /// they reach zero.
 ///
 /// The outstanding callback count automatically starts at 1.
 class OutstandingCallbackCounter {
   /// The number of outstanding callbacks.
   var _count = 1;
 
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   /// Removes all outstanding callbacks, forcing [noOutstandingCallbacks] to
   /// fire.
   ///
   /// Future calls to [addOutstandingCallback] and [removeOutstandingCallback]
   /// will be ignored.
   void removeAllOutstandingCallbacks() {
     if (!_completer.isCompleted) _completer.complete();
   }
 }