Yes two things were removed.
The old extension API and the even older “Custom functions” API (which you’re using in this case) was completely removed.
Sorry for the confusion.
The extension API has a little overhead when creating small functions like this but it’s worth it because once you have you can always extend it further. 
The code should work with little modification as an extension you just have to wrap it in a binding.
More info: How to create an extension
And feel free to ask me questions via pm
If you want I could also add this to the extension I have here https://discuss.eroscripts.com/t/11-lua-scripts-for-openfunscripter/23602/28?u=gagax123