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/Overlay.cpp b/src/Overlay.cpp
index 5a6ee04..3fdb554 100644
--- a/src/Overlay.cpp
+++ b/src/Overlay.cpp
@@ -14,8 +14,6 @@
 // limitations under the License.
 */
 
-#include "filesystem.hpp"
-
 #include <Overlay.hpp>
 #include <Utils.hpp>
 #include <boost/algorithm/string/predicate.hpp>
@@ -23,6 +21,7 @@
 #include <boost/container/flat_set.hpp>
 #include <boost/process/child.hpp>
 #include <devices.hpp>
+#include <filesystem>
 #include <iomanip>
 #include <iostream>
 #include <nlohmann/json.hpp>