[cleanup] Leftover audio transcoding plugins


And finally some floaters in the audio transcoding flow. 
<img width="705" alt="Screenshot 2025-05-31 at 3 30 30 PM" src="https://github.com/user-attachments/assets/322777c4-5270-44bc-8238-af006093fb32" />

_Originally posted by @jaybawk in https://github.com/jordanlambrecht/modular-tdarr-flows/issues/18#issuecomment-2925886197_
            