Don't fork on coutcome in compose
Don't fork on coutcome in compose

Delete the entire half of the proof where out = CFailed, which was a
subset of the out = CFinished m' rs case anyway.

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl