Well, as I said, they should have been cleaned out automatically, but if you install or remove kernels without using mjwd-kernel, then those will not be removed.
But I notice that I too still have leftover modules from 6.1 — I’ve been running 6.12 for quite a long time now — and @straycat’s post here-above suggests that there is indeed a problem. So I will post a Manjaro Development > QA thread about it. 
Thank you for noticing. 
Possibly with a single “rm -rf” if you know your shell-fu. 
Edit:
Here it is… 