Cleanup: remove non-standard retain_unknown_fields from .proto files

components/sync/protocol/password_specifics.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 datatype extension for password data.
 
 // 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;
 
 import "encryption.proto";
 
 // These are the properties that get serialized into the |encrypted| field of
 // PasswordSpecifics. They correspond to fields in autofill::PasswordForm.
 //
 // Sync unique tag is calculated as
 // EscapePath(origin) + "|" +
@@ skipping 88 matching lines @@
 
 // Properties of password sync objects.
 message PasswordSpecifics {
   // The actual password data. Contains an encrypted PasswordSpecificsData
   // message.
   optional EncryptedData encrypted = 1;
   // An unsynced field for use internally on the client. This field should
   // never be set in any network-based communications.
   optional PasswordSpecificsData client_only_encrypted_data = 2;
 }