audio/mp3: remove the mp3 package

[hajimehoshi]

Operating System

• [ ] Windows
• [ ] macOS
• [ ] Linux
• [ ] FreeBSD
• [ ] OpenBSD
• [ ] Android
• [ ] iOS
• [ ] Nintendo Switch
• [ ] Xbox
• [ ] Web Browsers

What feature would you like to be added?

As I no longer maintain the go-mp3 project, I would like to remove the audio/mp3 package in v3.

Why is this needed?

n/a

[misterunix]

Would be alright by me. Vorbis is still supported so removing mp3 would just require a bit of rewriting.