Get rid of all the library tags.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1580943003 .
diff --git a/lib/http_throttle.dart b/lib/http_throttle.dart
index 7cd95a6..a9e9e50 100644
--- a/lib/http_throttle.dart
+++ b/lib/http_throttle.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 http_throttle;
-
 import 'dart:async';
 
 import 'package:http/http.dart';