My WAG is the .rss files are related to exif data in some way, maybe related to establishing the make / model of camera used for photos.
No, they clearly have something to do with RSS, but that's a functionality that's gradually disappearing from the interwebs. More than any normal person wants to know about it:
https://www.vice.com/en_us/article/a3mm4z/the-rise-and-demise-of-rss
I think the semi-automatic "mobile view" that jalbum.net provides, rather than showing the album with its native skin, is still relying on RSS files, but I don't think it's used for anything else. And if you're using a modern, responsive skin, you should have the mobile view disabled, anyway.
I just tried deleting the RSS files in my config file. Upon relaunching jAlbum, album19.rss reappeared, so jAlbum thinks it needs it for something. But it certainly doesn't need the older versions.