Get rid of all the library tags.

lib/src/backend/closed_exception.dart

Index: lib/src/backend/closed_exception.dart
diff --git a/lib/src/backend/closed_exception.dart b/lib/src/backend/closed_exception.dart
index 0c9dcca2e5bc70eb0643fdc55eb227e139219cee..4432466c20829d2808d5b58cfc6da0dd67a9aaf4 100644
--- a/lib/src/backend/closed_exception.dart
+++ b/lib/src/backend/closed_exception.dart
@@ -2,8 +2,6 @@
 // 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 unittest.backend.closed_exception;
-
 /// An exception thrown by various front-end methods when the test framework has
 /// been closed and a test must shut down as soon as possible.
 class ClosedException implements Exception {