c++17: drop experimental::filesystem

Use the real filesystem library, and drop support for building with
experimental under c++14.

Signed-off-by: Jayanth Othayoth <ojayanth@in.ibm.com>
Change-Id: I730c0d6dce53b5e0aa0867cddb7f325cdb9b45fc
diff --git a/core_manager.cpp b/core_manager.cpp
index 19b80a2..9dfaa9b 100644
--- a/core_manager.cpp
+++ b/core_manager.cpp
@@ -2,7 +2,7 @@
 
 #include "core_manager.hpp"
 
-#include <experimental/filesystem>
+#include <filesystem>
 #include <phosphor-logging/log.hpp>
 #include <regex>
 #include <sdbusplus/exception.hpp>
@@ -23,8 +23,7 @@
 
     for (const auto& i : fileInfo)
     {
-        namespace fs = std::experimental::filesystem;
-        fs::path file(i.first);
+        std::filesystem::path file(i.first);
         std::string name = file.filename();
 
         /*