Use std::filesystem in favor of custom module

Reuse some code.  Fix a bug in the process.

Resolves openbmc/openbmc#1254

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Change-Id: I3fdbb70d6372f4a3193204bd2c9b6535315a3c70
diff --git a/Makefile.am b/Makefile.am
index 7bfb12a..b7057ad 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -7,6 +7,7 @@
 noinst_LTLIBRARIES = libhwmon.la
 libhwmon_la_LDFLAGS = -static
 libhwmon_la_LIBADD = \
+	-lstdc++fs \
 	$(SDBUSPLUS_LIBS) \
 	$(PHOSPHOR_DBUS_INTERFACES_LIBS) \
 	$(PHOSPHOR_LOGGING_LIBS)
@@ -17,7 +18,6 @@
 
 libhwmon_la_SOURCES = \
 	argument.cpp \
-	directory.cpp \
 	sensorset.cpp \
 	mainloop.cpp \
 	sysfs.cpp \