Remove support for Object.observe

test/mjsunit/es7/regress/regress-443982.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: --harmony-object-observe
-
-var records;
-function observer(r) {
-  records = r;
-}
-
-Object.defineProperty(Array.prototype, '0', {
-  get: function() { return 0; },
-  set: function() { throw "boom!"; }
-});
-arr = [1, 2];
-Array.observe(arr, observer);
-arr.length = 0;
-assertEquals(0, arr.length);
-
-Object.deliverChangeRecords(observer);
-assertEquals(1, records.length);
-assertEquals('splice', records[0].type);
-assertArrayEquals([1, 2], records[0].removed);