[RFC] Amiga/VMS cleanup

The removal of most items was pretty straightforward, but I have one question. I noticed that `runtime/doc/develop.txt` states this:
```
Function names can not be more than 31 characters long (because of VMS).
```
Does anyone know if this is still true? If it's not, I'd like to remove it.
Done for this line. Given there will probably be a lot of instances, I'll remove the rest in a later PR.