Get rid of #source in pub.

utils/pub/utils.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Generic utility functions. Stuff that should possibly be in core.
  */
-#library('pub_utils');
+#library('utils');
 
 /** Thrown by methods that parse text when the text isn't a valid. */
 class FormatException implements Exception {
   final String message;
 
   FormatException(this.message);
 
   String toString() => message;
 }
 
@@ skipping 44 matching lines @@
 /**
  * Asserts that [iter] contains only one element, and returns it.
  */
 only(Iterable iter) {
   var iterator = iter.iterator();
   assert(iterator.hasNext());
   var obj = iterator.next();
   assert(!iterator.hasNext());
   return obj;
 }