Revert "Add some support for the code-point code-unit distinction."

tests/corelib/reg_exp_unicode_2_test.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.
-// Dart test for testing regular expressions in Dart.
-
-// These tests currently fail due to bug 6592.
-main() {
-  String str = "\u{10000}";
-
-  // Dot should match a surrogate pair.
-  Expect.isTrue(new RegExp(r'^.$').hasMatch(str));
-
-  // Non-BMP characters in character classes should be treated as one character,
-  // not two separate surrogates.
-  String alias = "\u{10402}";  // 0xd801 0xdc02.
-  String char_class = "\u{10401}\u{10802}";  // 0xd801 0xdc01 0xd802 0xdc02.
-  Expect.isFalse(new RegExp('^[$char_class]+\$').hasMatch(alias));
-}