Switch to std::filesystem

Drop the dependency on Boost.Filesystem

Change-Id: I5d6f6fe38cd0cf1c6996221188fa63db146dc9f9
diff --git a/tools/ndnsec/main.cpp b/tools/ndnsec/main.cpp
index a9a055b..efdc526 100644
--- a/tools/ndnsec/main.cpp
+++ b/tools/ndnsec/main.cpp
@@ -26,7 +26,7 @@
 #include "ndn-cxx/version.hpp"
 
 #include <boost/exception/diagnostic_information.hpp>
-#include <boost/filesystem/path.hpp>
+#include <filesystem>
 #include <iostream>
 
 NDN_LOG_INIT(ndnsec);
@@ -54,8 +54,7 @@
 int
 main(int argc, char* argv[])
 {
-  boost::filesystem::path p(argv[0]);
-  std::string basename(p.filename().string());
+  std::string basename = std::filesystem::path(argv[0]).filename();
   std::string command;
   if (basename.rfind("ndnsec-", 0) == 0) {
     command = basename.substr(std::strlen("ndnsec-"));