Remove finalURL flag from Response idl file as per latest spec changes.

Source/modules/fetch/Response.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // http://fetch.spec.whatwg.org/#response-class
 
 enum ResponseType { "basic", "cors", "default", "error", "opaque" };
 
 // FIXME: Add union type: URLSearchParams
 typedef (Blob or ArrayBuffer or ArrayBufferView or FormData or USVString) BodyInit;
 
 [
     Constructor(optional BodyInit body, optional Dictionary responseInitDict),
     ConstructorCallWith=ExecutionContext,
     Exposed(Window GlobalFetch, DedicatedWorker GlobalFetch, SharedWorker GlobalFetch, ServiceWorker ServiceWorker),
     RaisesException=Constructor,
     ActiveDOMObject,
     GarbageCollected,
     TypeChecking=Interface,
 ] interface Response {
     // FIXME: Implement error();
     // FIXME: Implement redirect().
     readonly attribute ResponseType type;
     readonly attribute USVString url;
-    // FIXME: Implement attribute boolean finalURL;
     readonly attribute unsigned short status;
     readonly attribute boolean ok;
     readonly attribute ByteString statusText;
     readonly attribute Headers headers;
 
     [RaisesException] Response clone();
 
     // FIXME: Move this attribute into Body when the extended-attribute
     // is removed.
     [RuntimeEnabled=ExperimentalStream] readonly attribute ReadableStream body;
 };
 
 Response implements Body;