This script is a library script, which means that it is intended to be used by other scripts (similar to WaniKani Open Framework). It simplifies the addition of information to WaniKani items for userscripts like Keisei or Niai. I have created it because the recent change of the lesson page was breaking several userscripts (two of my own and several of other script authors), and instead of fixing them one by one, I wrote this library script and fixed all userscripts by letting them use WaniKani Item Info Injector instead of their previous injection method that was not working anymore.
That said, I don’t know why this script landed in your list of installed userscripts. It can be installed, but the only place where I linked to the Greasy Fork page was in the WaniKani Lesson Filter thread, and you would have had to manually install it. For now, all scripts just include it using the @require tag.
I have not created a thread for this library script yet, because there are still some things I want to change about it before I “advertise” it.
Anyway, you can uninstall the script, but you can also keep it. If it is installed like this, every other script uses this one (instead of their own @required one), so this setup makes sure that you always use the newest version with the latest bugfixes.