security: Rename security/v2/* to security/*

Security v1-v2 transition has been completed for a while and path
separation is no longer needed. However, this commit preserves
`ndn::security::v2` namespace, but makes it inline.

Some commonly used v2 headers are preserved, but are deprecated and
should be avoided in the dependent software.

Change-Id: I26056cb3d34bcdc0a16e06dea8c1a78c03da2d40
diff --git a/tools/ndnsec/cert-gen.cpp b/tools/ndnsec/cert-gen.cpp
index c526654..9aef677 100644
--- a/tools/ndnsec/cert-gen.cpp
+++ b/tools/ndnsec/cert-gen.cpp
@@ -22,11 +22,11 @@
 #include "ndnsec.hpp"
 #include "util.hpp"
 
+#include "ndn-cxx/security/additional-description.hpp"
 #include "ndn-cxx/security/transform/base64-encode.hpp"
 #include "ndn-cxx/security/transform/buffer-source.hpp"
 #include "ndn-cxx/security/transform/public-key.hpp"
 #include "ndn-cxx/security/transform/stream-sink.hpp"
-#include "ndn-cxx/security/v2/additional-description.hpp"
 
 namespace ndn {
 namespace ndnsec {