c++17: drop experimental::filesystem

Use std::filesystem, and drop support for building with experimental
under c++14.

Tested: Build the repo.
Change-Id: I4af0d9c034dbfef5a65153ba5447b86c961aebf1
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/phosphor-ldap-mapper/ldap_mapper_entry.cpp b/phosphor-ldap-mapper/ldap_mapper_entry.cpp
index 8410942..781833e 100644
--- a/phosphor-ldap-mapper/ldap_mapper_entry.cpp
+++ b/phosphor-ldap-mapper/ldap_mapper_entry.cpp
@@ -1,4 +1,4 @@
-#include <experimental/filesystem>
+#include <filesystem>
 #include <xyz/openbmc_project/Common/error.hpp>
 #include <xyz/openbmc_project/User/Common/error.hpp>
 #include <phosphor-logging/log.hpp>
@@ -25,8 +25,8 @@
                                  const std::string &privilege,
                                  LDAPMapperMgr &parent) :
     Ifaces(bus, path, true),
-    id(std::stol(std::experimental::filesystem::path(path).filename())),
-    manager(parent), persistPath(filePath)
+    id(std::stol(std::filesystem::path(path).filename())), manager(parent),
+    persistPath(filePath)
 {
     Ifaces::privilege(privilege, true);
     Ifaces::groupName(groupName, true);
@@ -36,8 +36,8 @@
 LDAPMapperEntry::LDAPMapperEntry(sdbusplus::bus::bus &bus, const char *path,
                                  const char *filePath, LDAPMapperMgr &parent) :
     Ifaces(bus, path, true),
-    id(std::stol(std::experimental::filesystem::path(path).filename())),
-    manager(parent), persistPath(filePath)
+    id(std::stol(std::filesystem::path(path).filename())), manager(parent),
+    persistPath(filePath)
 {
 }