Revert "Add native_testing library to mock @Native classes"

tests/compiler/dart2js_native/subclassing_2_test.dart

Index: tests/compiler/dart2js_native/subclassing_2_test.dart
diff --git a/tests/compiler/dart2js_native/subclassing_2_test.dart b/tests/compiler/dart2js_native/subclassing_2_test.dart
index a6b8bb30a0aa06b5e61cc54da56fea2cd96cf51c..4b9785c4e9118a22cff9b6b3af9adddc52a3e426 100644
--- a/tests/compiler/dart2js_native/subclassing_2_test.dart
+++ b/tests/compiler/dart2js_native/subclassing_2_test.dart
@@ -2,8 +2,8 @@
 // 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.
 
-import 'native_testing.dart';
-import 'dart:_js_helper' show setNativeSubclassDispatchRecord;
+import "package:expect/expect.dart";
+import 'dart:_js_helper' show Native, Creates, setNativeSubclassDispatchRecord;
 import 'dart:_interceptors' show findInterceptorForType;
 
 // Test calling convention of methods introduced on subclasses of native
@@ -37,7 +37,6 @@ getBPrototype = function(){return B.prototype;};
 """;
 
 main() {
-  nativeTesting();
   setup();
 
   setNativeSubclassDispatchRecord(getBPrototype(), findInterceptorForType(B));