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/tests/unit/unit-tests-pch.hpp b/tests/unit/unit-tests-pch.hpp
index 54e15f9..5f2ed67 100644
--- a/tests/unit/unit-tests-pch.hpp
+++ b/tests/unit/unit-tests-pch.hpp
@@ -27,7 +27,7 @@
 #include "ndn-cxx/face.hpp"
 #include "ndn-cxx/ims/in-memory-storage.hpp"
 #include "ndn-cxx/security/transform.hpp"
-#include "ndn-cxx/security/v2/validator.hpp"
+#include "ndn-cxx/security/validator.hpp"
 #include "ndn-cxx/util/config-file.hpp"
 
 #include "tests/identity-management-fixture.hpp"