Byrnorthil

You can find the default world save under VintagestoryData/Saves/default.vcdbs. You could simply delete this file and either let the server make a new one or import one from your own pc, but you don't have to do that either.
If you go into the serverconfig.json file and edit the SaveFileLocation parameter, you can specify a new world name and the server will simply leave the old one there. If you're constrained by storage space you might want to delete the old file, but other than that it's totally fine to just leave your old save there in case you want to archive or revisit it later.

I did some messing around and the best I can discern is that these setting were probably entirely retired some time ago and the wiki is simply outdated. Keep in mind that all the worldconfigcreate command does is add a line of text to your config file; the game's acknowledgement that it was done successfully doesn't mean anything if the game code doesn't recognize that line of text as a legitimate setting. You could do something like this:
 
/worldconfigcreate string asdf "ligma balls" and the game would let you do it just fine, but the new asdf setting you just created would have no impact on the game.