Reinstate group_red_aux subproof in ecdsa-crucible.saw.
Reinstate group_red_aux subproof in ecdsa-crucible.saw.

It was previously stubbed out to avoid a bug that no longer occurs.

GaloisInc/saw-script,GaloisInc/saw-script,GaloisInc/saw-script,GaloisInc/saw-script,GaloisInc/saw-script