Deprecating tracked_directories as a Vault parameter

vault_keyset.proto

 // Copyright (c) 2009 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.
 
 package cryptohome;
 
 message SerializedVaultKeyset {
   enum Flags {
     NONE = 0;
     TPM_WRAPPED = 1;
     SCRYPT_WRAPPED = 2;
   }
   required int32 flags = 1;
   required bytes salt = 2;
   required bytes wrapped_keyset = 3;
   optional bytes tpm_key = 4;
   optional bytes tpm_public_key_hash = 5;
   optional int32 password_rounds = 6;
-  repeated string tracked_subdirectories = 7;
+  repeated string deprecated_tracked_subdirectories = 7;
 }