Remove previously deprecated headers, methods, and constants

Change-Id: I3e809e25c8f2bc2ae0f027413d9e0161245353c6
Refs: #3988
diff --git a/src/signature.hpp b/src/signature.hpp
index 362e172..4644807 100644
--- a/src/signature.hpp
+++ b/src/signature.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2016 Regents of the University of California.
+ * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -43,13 +43,6 @@
     }
   };
 
-  /// @deprecated use tlv::SignatureTypeValue instead.
-  enum {
-    Sha256 = tlv::DigestSha256,
-    Sha256WithRsa = tlv::SignatureSha256WithRsa,
-    Sha256WithEcdsa = tlv::SignatureSha256WithEcdsa
-  };
-
   Signature() = default;
 
   explicit