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

tests/compiler/dart2js_native/native_call_arity1_frog_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.
 
 import "dart:_js_helper";
 import "package:expect/expect.dart";
 
 // Test that native methods with unnamed* optional arguments are called with the
 // number of arguments in the call site.  This is necessary because native
 // methods can dispatch on the number of arguments.  Passing null or undefined
 // as the last argument is not the same as passing one fewer argument.
 //
 // * Optional positional arguments are passed in the correct position, so
 // require preceding arguments to be passed.
 
 @Native("A")
 class A {
   int foo(int x) native;
 }
 
 @Native("B")
 class B {
   int foo([x, y, z]) native;
 }
 
 // TODO(sra): Add a case where the parameters have default values.  Wait until
 // dart:html need non-null default values.
 
-A makeA() native { return new A(); }
-B makeB() native { return new B(); }
+A makeA() native;
+B makeB() native;
 
 void setup() native """
 function A() {}
 A.prototype.foo = function () { return arguments.length; };
 
 function B() {}
 B.prototype.foo = function () { return arguments.length; };
 
 makeA = function(){return new A;};
 makeB = function(){return new B;};
@@ skipping 33 matching lines @@
   Expect.equals(3, b.foo(10, 20, 30));
 
   Expect.throws(() => b.foo(10, 20, 30, 40));
 }
 
 main() {
   setup();
   testDynamicContext();
   testStaticContext();
 }