Remove more dead code after Object.observe removal

src/js/prologue.js

 // Copyright 2015 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.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 178 matching lines @@
     "MakeError",
     "MakeRangeError",
     "MakeTypeError",
     "MapEntries",
     "MapIterator",
     "MapIteratorNext",
     "MaxSimple",
     "MinSimple",
     "NumberIsInteger",
     "ObjectDefineProperty",
-    "ObserveArrayMethods",
-    "ObserveObjectMethods",
     "PromiseChain",
     "PromiseDeferred",
     "PromiseResolved",
     "RegExpSubclassExecJS",
     "RegExpSubclassMatch",
     "RegExpSubclassReplace",
     "RegExpSubclassSearch",
     "RegExpSubclassSplit",
     "RegExpSubclassTest",
     "SetIterator",
@@ skipping 144 matching lines @@
 
 extrasUtils.uncurryThis = function uncurryThis(func) {
   return function(thisArg, ...args) {
     return %reflect_apply(func, thisArg, args);
   };
 };
 
 %ToFastProperties(extrasUtils);
 
 })