libexec/klab-prove-all: unaccept BADGAS specs

[asymmetric]

Remove them from the accept directory, so that the whole process is restarted.

This is not ideal (since the proof had already been accepted), but the
alternative risks giving false positives if one doesn't inspect the
build log.

[d-xo]

Do we know why get-gas was unable to extract a gas expression from these BADGAS proofs? i.e was the problem in the proof or in get-gas itself?

[asymmetric]

Nope, I don't know, but I would say that's out of scope for this PR, isn't it?

If you look at get-gas and get-x, there are several reasons why they could exit with an error, some of them unrecoverable (e.g. files missing, maybe someone has removed them manually?), and this PR tries to recover from that state without manual intervention.

[asymmetric]

But I do think this is not the best solution, since the proofs itself has been accepted, so I'm open to better suggestions.