data: add shortcuts to access SignatureType and KeyLocator

Also, modernize the API of SignatureInfo and deprecate
unsetKeyLocator() and unsetValidityPeriod()

Change-Id: I8b775a4deb185784a3dcc8bd96c8f5f0c2915854
diff --git a/tests/unit/security/v2/validator.t.cpp b/tests/unit/security/v2/validator.t.cpp
index 934492f..b5a7e04 100644
--- a/tests/unit/security/v2/validator.t.cpp
+++ b/tests/unit/security/v2/validator.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2018 Regents of the University of California.
+ * Copyright (c) 2013-2020 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -316,8 +316,8 @@
     request.setName(Name(key.getName()).append("looper").appendVersion());
 
     SignatureInfo info;
-    info.setValidityPeriod({time::system_clock::now() - 100_days,
-                            time::system_clock::now() + 100_days});
+    info.setValidityPeriod(ValidityPeriod(time::system_clock::now() - 100_days,
+                                          time::system_clock::now() + 100_days));
     m_keyChain.sign(request, signingByKey(signer).setSignatureInfo(info));
     m_keyChain.addCertificate(key, request);