Cleanup: remove non-standard retain_unknown_fields from .proto files

components/sync/protocol/autofill_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 autofill.
 
 // 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;
 
 // Properties of autofill sync objects.
 
 // An AutofillProfile.
 message AutofillProfileSpecifics {
   optional string guid = 15;
   optional string origin = 16;
   optional int64 use_count = 22;
@@ skipping 180 matching lines @@
   // - Language code
   optional string id = 2;
 
   // The number of times that this Wallet card or address was used.
   optional int64 use_count = 3;
 
   // The last use date of this Wallet card or address. Measured in microseconds
   // since the Windows epoch (1601).
   optional int64 use_date = 4;
 }