Remove stale files from lib/html/src.

lib/html/src/DocumentFragment.dart

Index: lib/html/src/DocumentFragment.dart
diff --git a/lib/html/src/DocumentFragment.dart b/lib/html/src/DocumentFragment.dart
deleted file mode 100644
index b1fc9c575ff785c8fc8b75336512a0c8fa1da74f..0000000000000000000000000000000000000000
--- a/lib/html/src/DocumentFragment.dart
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright (c) 2011, 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.
-
-interface DocumentFragment extends Element default DocumentFragmentWrappingImplementation {
- 
-  DocumentFragment();
-
-  DocumentFragment.html(String html);
-
-  /** WARNING: Currently this doesn't work on Dartium (issue 649). */
-  DocumentFragment.xml(String xml);
-
-  DocumentFragment.svg(String svg);
-
-  DocumentFragment clone(bool deep);
-}