Remove references to experimental filesystem

We're at CPP17 everywhere now, no need to keep the
experimental refrerence.

Tested: It builds

Change-Id: I2a3d13ff806261a47da0493be2f24a2b0c361c9f
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/src/EntityManager.cpp b/src/EntityManager.cpp
index a71d553..57c9fda 100644
--- a/src/EntityManager.cpp
+++ b/src/EntityManager.cpp
@@ -16,8 +16,6 @@
 
 #include "EntityManager.hpp"
 
-#include "filesystem.hpp"
-
 #include <Overlay.hpp>
 #include <Utils.hpp>
 #include <VariantVisitors.hpp>
@@ -27,6 +25,7 @@
 #include <boost/container/flat_map.hpp>
 #include <boost/container/flat_set.hpp>
 #include <boost/lexical_cast.hpp>
+#include <filesystem>
 #include <fstream>
 #include <iostream>
 #include <nlohmann/json.hpp>