security: dissolve private header security/impl/openssl.hpp

It no longer serves a purpose

Change-Id: Ic145460c139dbda969976644352fed3f44fd32ec
diff --git a/tests/unit/security/signing-info.t.cpp b/tests/unit/security/signing-info.t.cpp
index a68c031..87c347f 100644
--- a/tests/unit/security/signing-info.t.cpp
+++ b/tests/unit/security/signing-info.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2021 Regents of the University of California.
+ * Copyright (c) 2013-2022 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -20,10 +20,10 @@
  */
 
 #include "ndn-cxx/security/signing-info.hpp"
-#include "ndn-cxx/security/impl/openssl.hpp"
 
 #include "tests/boost-test.hpp"
 
+#include <openssl/opensslv.h>
 #include <boost/lexical_cast.hpp>
 #include <sstream>