Remove old frog-style dummy bodies from dart2js native class tests

tests/compiler/dart2js_native/native_closure_identity_frog_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.
 
 import "dart:_js_helper";
 import "package:expect/expect.dart";
 
 typedef void MyFunctionType();
 
 @Native("A")
 class A {
   setClosure(MyFunctionType f) native;
   check(MyFunctionType f) native;
   invoke() native;
 }
 
-makeA() native { return new A(); }
+makeA() native;
 
 void setup() native """
 function A() {}
 A.prototype.setClosure = function(f) { this.f = f; };
 A.prototype.check = function(f) { return this.f === f; };
 A.prototype.invoke = function() { return this.f(); };
 makeA = function(){return new A;};
 """;
 
 var staticClosure;
@@ skipping 37 matching lines @@
 
   checkUntyped(makeA(), b.instanceMethod);
   checkTyped(makeA(), b.instanceMethod);
 
   checkUntyped(makeA(), closureStatement);
   checkTyped(makeA(), closureStatement);
 
   checkUntyped(makeA(), closureExpression);
   checkTyped(makeA(), closureExpression);
 }