Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/window_test.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.
 
-library WindowTest;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
 import 'dart:html';
 
+import 'package:expect/minitest.dart';
+
 main() {
-  useHtmlConfiguration();
-
   test('scrollXY', () {
     expect(window.scrollX, 0);
     expect(window.scrollY, 0);
   });
 }