Remove a regression test that depended on utils.ImportNow()

The test itself was for an issue that's handled statically since
https://codereview.chromium.org/1302313013 (we were missing some
instance types in a switch statement).

This leaves us with only a single test that depends on the JS
native import system.

R=littledan@chromium.org

Review-Url: https://codereview.chromium.org/2707133005
Cr-Commit-Position: refs/heads/master@{#43393}

src/js/prologue.js

@@ -169,11 +169,9 @@ function PostNatives(utils) {
   var expose_list = [
     "FormatDateToParts",
     "MapEntries",
-    "MapIterator",
     "MapIteratorNext",
     "MaxSimple",
     "MinSimple",
-    "SetIterator",
     "SetIteratorNext",
     "SetValues",
     "ToLocaleLowerCaseI18N",

test/mjsunit/regress/regress-3281.js

-// Copyright 2014 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --expose-natives-as=builtins
-// Should not crash or raise an exception.
-
-var SetIterator = builtins.ImportNow("SetIterator");
-var s = new Set();
-var setIterator = new SetIterator(s, 2);
-
-var MapIterator = builtins.ImportNow("MapIterator");
-var m = new Map();
-var mapIterator = new MapIterator(m, 2);