ipmid: replace std::experimental::optional with std::optional

Now that the project is using c++17, std::optional can be used directly
instead of via the std::experimental way.

Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
Change-Id: I7087f58bd3d9fd90b8b31e6902554351a3db2d0f
diff --git a/utils.hpp b/utils.hpp
index 8b69b09..a100718 100644
--- a/utils.hpp
+++ b/utils.hpp
@@ -1,7 +1,7 @@
 #pragma once
 #include "types.hpp"
 
-#include <experimental/optional>
+#include <optional>
 #include <sdbusplus/server.hpp>
 
 namespace ipmi
@@ -76,9 +76,9 @@
     /** @brief DBUS path provided by the service */
     const std::string path;
     /** @brief The name of the service if valid */
-    std::experimental::optional<std::string> cachedService;
+    std::optional<std::string> cachedService;
     /** @brief The name of the bus used in the service lookup */
-    std::experimental::optional<std::string> cachedBusName;
+    std::optional<std::string> cachedBusName;
 };
 
 /**