Cleanup: remove non-standard retain_unknown_fields from .proto files

components/sync/protocol/typed_url_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 typed urls.
 
 // 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 typed_url sync objects - fields correspond to similarly named
 // fields in history::URLRow.
 message TypedUrlSpecifics {
   // Actual URL that was typed.
   optional string url = 1;
   // Title of the page corresponding to this URL.
   optional string title = 2;
   // The number of times this URL was typed. Deprecated since we no longer sync
   // this information (it's inferred by the history code from the transition
   // type for each visit).
   // optional int32 typed_count = 3; (deprecated)
   // True if the URL should be used for auto-complete.
   optional bool hidden = 4;
   // The number of visits (includes page reloads).
   // repeated int64 visit = 5; (deprecated)
   // The number of explicit navigations to this URL (excludes page reloads) -
   // deprecated as we no longer sync this (history code infers this from the
   // |visits| array).
   // optional int32 visited_count = 6; (deprecated)
   // Timestamps for all visits to this URL.
   repeated int64 visits = 7 [packed = true];
   // The PageTransition::Type for each of the visits in the |visit| array. Both
   // arrays must be the same length.
   repeated int32 visit_transitions = 8 [packed = true];
 }