Remove page_ordinal from AppListSpecifics.

sync/protocol/app_list_specifics.proto

 // Copyright 2013 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.
 //
 // Sync protocol datatype extension for the app list (aka app launcher).
 
 // Update proto_{value,enum}_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 23 matching lines @@
     TYPE_URL = 4;
   }
   optional AppListItemType item_type = 2;
 
   // Item name (FOLDER or URL).
   optional string item_name = 3;
 
   // Id of the parent (folder) item.
   optional string parent_id = 4;
 
+  // Marked OBSOLETE because this is unused for the app list.
   // Which page this item will appear on in the app list.
-  optional string page_ordinal = 5;
+  optional string OBSOLETE_page_ordinal = 5 [deprecated = true];
 
   // Where on a page this item will appear.
   optional string item_ordinal = 6;
 }