adding missing DELEG predicate failures to spec

[JaredCorduan]

The formal spec listed only 7 predicate failures for the DELEG rule, but the implementation contained 11 (which did include the 7).

• The predicate StakeKeyInRewards should actually be removed. It is redundant with StakeKeyAlreadyRegistered (we removed the stkCreds mapping from the implementation in remove stkcreds and stpools #1683 and from the spec in Remove the now irrelevant maps stkCreds and stpools from the formal spec #1692, making the reward mapping the source of truth for registered stake credentials). Unfortunately, we are using StakeKeyInRewards in the place where StakeKeyAlreadyRegistered is the more helpful name. I have made a TODO in the implementation to replace StakeKeyInRewards with StakeKeyAlreadyRegistered when there is a good time (right now is not).
• I added StakeKeyNonZeroAccountBalance, MIRCertificateTooLateInEpoch, and DuplicateGenesisVRF to the spec.

closes #1719