Linux: change protobuf default option to allow building

sync/protocol/sync_enums.proto

 // Copyright (c) 2012 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 for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
 
-option optimize_for = LITE_RUNTIME;
-option retain_unknown_fields = true;
-
 package sync_pb;
 
 message SyncEnums {
   // These events are sent by |SyncManager| class. Note: In the code they each
   // of these events have some additional info but we are not sending them to
   // server.
   enum EventType {
     AUTH_ERROR = 1; // Auth error. Note this gets generated even during
                     // successful auth with the error set to none.
     UPDATED_TOKEN = 2; // Client received an updated token.
@@ skipping 83 matching lines @@
   enum DeviceType {
     TYPE_WIN = 1;
     TYPE_MAC = 2;
     TYPE_LINUX = 3;
     TYPE_CROS = 4;
     TYPE_OTHER = 5;
     TYPE_PHONE = 6;
     TYPE_TABLET = 7;
   }
 }