signature: deprecate Signature in favor of SignatureInfo

The Signature in Data packets and Certificates
has been deprecated in favor of separate objects
representing the Signature info and value.

Also deprecate type-specific Signature helpers.

refs #4804

Change-Id: Iab5b5c618e75cc11d31801d86a89a550a6add7a0
diff --git a/tests/unit/security/digest-sha256.t.cpp b/tests/unit/security/digest-sha256.t.cpp
index d3fcf4a..8b5e11d 100644
--- a/tests/unit/security/digest-sha256.t.cpp
+++ b/tests/unit/security/digest-sha256.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).
  *
@@ -53,7 +53,7 @@
   testData.setContent(reinterpret_cast<uint8_t*>(content), 5);
   m_keyChain.sign(testData, security::SigningInfo(security::SigningInfo::SIGNER_TYPE_SHA256));
 
-  BOOST_CHECK_THROW(testData.getSignature().getKeyLocator(), ndn::SignatureInfo::Error);
+  BOOST_CHECK_THROW(testData.getSignatureInfo().getKeyLocator(), ndn::SignatureInfo::Error);
   verifyDigest(testData, DigestAlgorithm::SHA256);
 }