Drop simple and single+simple slot normaliziation styles

I dropped simple & simple+single slot normalization styles.

(I've also found simple+single normalization style used on one of our internal projects and changed it to single).

I've added some comments. It seems this functinoality was not covered by tests, what sucks. It would be nice to add a short test-case to prove single-slot normalization still works correctly, but I guess that would be best a separate issue and is less important. Still, at least let's add the issue?

this will need a change record, please prepare a draft

Done:

• Created followup 📌 Add test for single-slot normalization style Active
• Created draft CR. Just said "there is no replacement", as I cannot infer from just the code in the normalizer, how things exactly come out / whether there is a way to get the exact same result.
• Implemented requested changes (with one comment just to be sure, because see previous point).

Automatically closed - issue fixed for 2 weeks with no activity.