[BackgroundSync Cleanup] Remove periodic sync code

content/browser/background_sync/background_sync.proto

 // Copyright 2015 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package content;
 
 enum SyncNetworkState {
   NETWORK_STATE_ANY = 0;
   NETWORK_STATE_AVOID_CELLULAR = 1;
   NETWORK_STATE_ONLINE = 2;
 }
 
-enum SyncPeriodicity {
-  SYNC_PERIODIC = 0;
-  SYNC_ONE_SHOT = 1;
-}
-
 message BackgroundSyncRegistrationProto {
   required int64 id = 1;
   required string tag = 2;
-  required SyncPeriodicity periodicity = 3;
-  required int64 min_period = 4;
+  // required SyncPeriodicity periodicity = 3;
+  // required int64 min_period = 4;
   required SyncNetworkState network_state = 5;
   // required SyncPowerState power_state = 6;
   required int32 num_attempts = 7;
   required int64 delay_until = 8;
 }
 
 message BackgroundSyncRegistrationsProto {
   repeated BackgroundSyncRegistrationProto registration = 1;
   required int64 next_registration_id = 2;
   required string origin = 3;
 }