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/test/Makefile.am b/test/Makefile.am
index fc6b72e..03c918e 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -18,8 +18,7 @@
           $(PHOSPHOR_DBUS_INTERFACES_LIBS) \
           $(PHOSPHOR_LOGGING_LIBS) \
           $(SDBUSPLUS_LIBS) \
-          -lcrypt \
-          -lstdc++fs
+          -lcrypt
 
 check_PROGRAMS = ldap_config_test
 ldap_config_test_CPPFLAGS = $(cppflags)