Missing storage space due to 2gb 'system data' - how to remove?
"System data" is... Well, the data that you need for your system to run. They are the files in your /system directory. You need those files there, otherwise you'd have a brick; your phone would be unusable without an operating system. A factory reset does not remove it because it only removes all user data (all files stored in /data directory.

Also, you may be confused as to why the total storage doesn't add up to 32GB. Hardware manufacturers refer to a GB as 1000 MB, which is 1000 KB, which is 1000 B. So there is a disparity here that gets bigger, the higher the number.