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

It no longer serves a purpose

Change-Id: Ic145460c139dbda969976644352fed3f44fd32ec
diff --git a/tests/unit/security/tpm/back-end.t.cpp b/tests/unit/security/tpm/back-end.t.cpp
index 9101aa3..e6f78e7 100644
--- a/tests/unit/security/tpm/back-end.t.cpp
+++ b/tests/unit/security/tpm/back-end.t.cpp
@@ -22,7 +22,6 @@
 #include "ndn-cxx/security/tpm/back-end.hpp"
 
 #include "ndn-cxx/encoding/buffer-stream.hpp"
-#include "ndn-cxx/security/impl/openssl.hpp"
 #include "ndn-cxx/security/pib/key.hpp"
 #include "ndn-cxx/security/transform/bool-sink.hpp"
 #include "ndn-cxx/security/transform/buffer-source.hpp"
@@ -38,6 +37,7 @@
 
 #include "tests/boost-test.hpp"
 
+#include <openssl/opensslv.h>
 #include <boost/mpl/vector.hpp>
 #include <set>