Remove prover_snapshots and generate in release flow

[jordancarlin]

Now that we have a system for generating releases with various attachments, we should remove the (very outdated) prover_snapshots directory and have the release process create and attach the output for each theorem prover.

Currently prover_snapshots contains

• coq
• hol4
• isabelle

[Timmmm]

Oh I assumed they were there because the process of creating them is difficult in some way. What exactly are they anyway?

[jordancarlin]

Correct me if I'm wrong @Alasdair or @bacam, but I believe they are just the output of make for those different targets? With an additional script or two and a little bit of documentation?

[bacam]

Yes, they're builds together with the supporting library from the version of Sail that produced them. Also, they're very out-of-date and likely to confuse people, so I agree with removing them.

Regarding building them; they all need a development version of Sail at the moment due to various bugs that recent versions of the model trigger. Isabelle also needs some updates to the handwritten files, which should hopefully stop bitrotting once we're using Alasdair's new configuration scheme. They all need some adaption to cmake (although I'm quite tempted to just rename Makefile.old to Makefile.provers and cut out all of the other bits...)