remove std::experimental usage

All of the std::experimental usages in this repository have a well
supported counterpart in std as of C++17.  Switch to use them.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I4cdf5cd27053ce85c7f70c215ee9456f96f79f42
diff --git a/src/event_manager.cpp b/src/event_manager.cpp
index 874c5a8..c52a96e 100644
--- a/src/event_manager.cpp
+++ b/src/event_manager.cpp
@@ -21,7 +21,7 @@
 #include "event.hpp"
 #include "event_serialize.hpp"
 
-#include <experimental/filesystem>
+#include <filesystem>
 
 namespace phosphor
 {
@@ -35,7 +35,7 @@
                      const std::string& propertyValue)
 {
     using namespace std::string_literals;
-    namespace fs = std::experimental::filesystem;
+    namespace fs = std::filesystem;
 
     auto msg = eventMessage;
     std::vector<std::string> additionalData;