Luarocks: Cleanup

The formula is a mess. I’m not sure why the stable block was necessary any more, upstream aren’t going to move on the install target check so there’s no risk of the patch becoming obsolete any time soon.

This PR is pretty much just to make reading the Luarocks formula a little more pleasant for everyone (And me). Nothing more fancy than that for now.

It also turns out Luarocks is using the system OpenSSL to check download MD5Sums. I’m not sure whether this merits an additional dependency or not. My gut says no, but equally I squirm at using the system OpenSSL for anything. I’ll leave the OpenSSL point open to discussion. Meh.

(*Side note - Why are you still using MD5Sums Luarocks? Seriously?*)
Would be good to try and remove this patch and fix stuff up on our side to match what `luarocks` expects.