Sunsetting select LibAFL crates

[addisoncrump]

We no longer want to support some crates; the technical debt currently blocking CI is just too much to handle. For example: the concolic support has largely gone unused, and no current maintainer is a code owner for this. What other crates should we delete?

[addisoncrump]

Please consider this issue also a place to voice that you still use a crate, and if you'd be willing to help maintain it.