Cleanup of lang/racket and racket-minimal.

• Reformat with portfmt
• Reduce diff between Racket ports
• Fix some portlint warnings
• Fix typo in --enable-ffi (it was just -enable-ffi before)
• Now FUTURES is enabled in lang/racket too

Update licensing information as per upstream announcement:

https://blog.racket-lang.org/2019/11/completing-racket-s-relicensing-effort.html