Revert "Make Array.prototype.pop throw if the last element is not configurable."

src/array.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 412 matching lines @@
   if (n == 0) {
     this.length = n;
     return;
   }
 
   if (%IsObserved(this))
     return ObservedArrayPop.call(this, n);
 
   n--;
   var value = this[n];
-  Delete(this, ToName(n), true);
+  delete this[n];
   this.length = n;
   return value;
 }
 
 
 function ObservedArrayPush() {
   var n = TO_UINT32(this.length);
   var m = %_ArgumentsLength();
 
   try {
@@ skipping 1208 matching lines @@
   ));
 
   SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();