Remove redundant call to Serialize() in ConfigItem::Commit()

The very same object is already serialized a few lines above, the result is
even stored in a variable, but that variable was not used before. Simply using
this variable results in a noticeable improvement of config validation times.

lib/config/configitem.cpp

@@ -288,7 +288,7 @@ ConfigObject::Ptr ConfigItem::Commit(bool discard)
 	Dictionary::Ptr persistentItem = new Dictionary({
 		{ "type", type->GetName() },
 		{ "name", GetName() },
-		{ "properties", Serialize(dobj, FAConfig) },
+		{ "properties", serializedObject },
 		{ "debug_hints", dhint },
 		{ "debug_info", new Array({
 			m_DebugInfo.Path,