Remove GenDelegs and IRewards from the state

[lehins]

We should have at least dropped contents of those fields during translation to Conway, but they aren't that big, so it is not really a problem. In fact Irewards should be empty anyways and GenDelgs should contain a Map with 7 elements in it.

That beind said, those concepts have been removed in Conway, so there is no reason for them to be hanging around in the ledger state going forward.

The proper fix for this is to move those fields into some part of the ledger state that has been changed in Conway (like GovState). If that is not possible we can figure out a new field in the ledger state that these guys could migrate to for pre-Conway eras.

[lehins]

This is very much related if not a duplicate of #4694