You can find a description of what has happened in 3.10 at
http://wiki.squeak.org/squeak/5975

In particular, look at the first link, because almost all the deletion
happened at the very beginning.  Unfortunately, the first link is more
a discussion of the various experiments that Edgar was trying, rather
than a description of what he eventually did.  I believe that
CandidatesForGo is a description of what he finallly did, and you will
find it near the end of that page.

Once you figure out what needs to be reloaded to make MP3s work,
please consider turning it all into a package and putting it in
Package Universe so that other people can easily load it.

Thanks!

-Ralph