Removed obsolete code

utils/css/cssselectorexception.dart

-// 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.
-
-// TODO(terry): Rename CompilerException to be SourceException then this
-//              exception would be derived from SourceException.
-
-/** Can be thrown on any Css runtime problem includes source location. */
-class CssSelectorException implements Exception {
-  final String _message;
-  final SourceSpan _location;
-
-  CssSelectorException(this._message, [this._location = null]);
-
-  String toString() {
-    if (_location != null) {
-      return 'CssSelectorException: ${_location.toMessageString(_message)}';
-    } else {
-      return 'CssSelectorException: $_message';
-    }
-  }
-
-}