Eliminate htmlescape package.

pkg/htmlescape/lib/htmlescape.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.
-
-/**
- * This library contains functions to escape strings for safe inclusion
- * in HTML source.
- */
-library htmlescape;
-
-/**
- * Escapes HTML-special characters of [text] so that the result can be
- * included verbatim in HTML source code, either in an element body or in an
- * attribute value.
- */
-String htmlEscape(String text) {
-  // TODO(efortuna): A more efficient implementation.
-  return text.replaceAll("&", "&")
-             .replaceAll("<", "&lt;")
-             .replaceAll(">", "&gt;")
-             .replaceAll('"', "&quot;")
-             .replaceAll("'", "&apos;");
-}