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.hpp b/host_state_manager.hpp
index 0e796f5..1e9bb10 100644
--- a/host_state_manager.hpp
+++ b/host_state_manager.hpp
@@ -13,7 +13,7 @@
 #include <xyz/openbmc_project/State/Boot/Progress/server.hpp>
 #include <xyz/openbmc_project/State/OperatingSystem/Status/server.hpp>
 
-#include <experimental/filesystem>
+#include <filesystem>
 #include <functional>
 #include <string>
 
@@ -33,7 +33,7 @@
 PHOSPHOR_LOG2_USING;
 
 namespace sdbusRule = sdbusplus::bus::match::rules;
-namespace fs = std::experimental::filesystem;
+namespace fs = std::filesystem;
 
 /** @class Host
  *  @brief OpenBMC host state management implementation.