Cleanup: remove non-standard retain_unknown_fields from .proto files

components/sync/protocol/data_type_state.proto

 // Copyright 2016 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
-option retain_unknown_fields = true;
 
 package sync_pb;
 
 import "sync.proto";
 
 // Sync proto to store data type global metadata in model type storage.
 message DataTypeState {
   // The latest progress markers received from the server.
   optional DataTypeProgressMarker progress_marker = 1;
 
   // A data type context.  Sent to the server in every commit or update
   // request.  May be updated by either responses from the server or requests
   // made on the model thread.  The interpretation of this value may be
   // data-type specific.  Many data types ignore it.
   optional DataTypeContext type_context = 2;
 
   // This value is set if this type's data should be encrypted on the server.
   // If this key changes, the client will need to re-commit all of its local
   // data to the server using the new encryption key.
   optional string encryption_key_name = 3;
 
   // This flag is set to true when the first download cycle is complete.  The
   // ModelTypeProcessor should not attempt to commit any items until this
   // flag is set.
   optional bool initial_sync_done = 4;
 }