Cleanup: remove non-standard retain_unknown_fields from .proto files

components/sync/protocol/history_status.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;
 
 message HistoryStatusRequest {}
 
 // Response to a history status request.
 message HistoryStatusResponse {
   // Minimal time to wait before issuing another request.
   optional int32 min_poll_interval_seconds = 1 [default = 3600];
 
   // Indicates whether the history corpuses have any derived data for a user.
   optional bool has_derived_data = 2;
 }