* Modify comment to only include 4844
Capella only modifies per epoch processing by adding
`process_historical_summaries_update`, which does not change the realization of
justification or finality.
Whilst 4844 does not currently modify realization, the spec is not yet final
enough to say that it never will.
* Clarify address change verification comment
The verification of the address change doesn't really have anything to do with
the current epoch. I think this was just a copy-paste from a function like
`verify_exit`.
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