Remove references to experimental filesystem

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

Change-Id: Ifd6af23c9bd8e40061b444436943c5192f9fc3e8
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/src/HwmonTempMain.cpp b/src/HwmonTempMain.cpp
index 430793a..eacfa2a 100644
--- a/src/HwmonTempMain.cpp
+++ b/src/HwmonTempMain.cpp
@@ -14,13 +14,12 @@
 // limitations under the License.
 */
 
-#include "filesystem.hpp"
-
 #include <HwmonTempSensor.hpp>
 #include <Utils.hpp>
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/container/flat_set.hpp>
+#include <filesystem>
 #include <fstream>
 #include <regex>
 #include <sdbusplus/asio/connection.hpp>