filesystem: use non-experimental version

std::experimental::filesystem has been deprecated since at least
C++17.  Switch to the std::filesystem one.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I7717a804a3d5c96f8717764c088529d65ad4e96c
diff --git a/host_state_manager_main.cpp b/host_state_manager_main.cpp
index 186e06b..b96cdbf 100644
--- a/host_state_manager_main.cpp
+++ b/host_state_manager_main.cpp
@@ -8,7 +8,7 @@
 
 #include <cstdlib>
 #include <exception>
-#include <experimental/filesystem>
+#include <filesystem>
 #include <iostream>
 
 int main(int argc, char** argv)
@@ -33,7 +33,7 @@
         }
     }
 
-    namespace fs = std::experimental::filesystem;
+    namespace fs = std::filesystem;
 
     auto bus = sdbusplus::bus::new_default();