Cleanup: remove non-standard retain_unknown_fields from .proto files

components/sync/protocol/wifi_credential_specifics.proto

 // Copyright 2014 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 WiFi credentials.
 
 // Update proto_{value,enum}_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 WiFi credential objects.
 message WifiCredentialSpecifics {
   optional bytes ssid = 1;  // Not necessarily UTF-8. May contain NUL.
 
   enum SecurityClass {
     SECURITY_CLASS_INVALID = 0;
     SECURITY_CLASS_NONE = 1;
@@ skipping 25 matching lines @@
   //   WPA/WPA-2 PSK as per IEEE 802.11i.
   // - A 64 character hex string. The string maps to the PSK per
   //   simple hex decoding.
   //
   // Note that, although the passphrase "should" contain only ASCII
   // characters, we represent |passphrase| as |bytes| rather than
   // |string|. This is to accomodate networks that use non-ASCII
   // passphrases.
   optional bytes passphrase = 3;
 }