chore: Remove deprecated protobuf fields

[dsarlis]

Several fields regarding storing Cycles prepayments are now obsolete after introducing new versions of them that deal with CompoundCycles. The relevant code has been deployed to production for a couple weeks already so we can now remove the fallback code that was trying to backfill data from the old fields.

Additionally, we make the parsing code for a new field prepayment_for_call_transmission that was introduced stricter as it should also be populated now in production.

[github-actions]

Run on f49d15b URL: https://github.com/dfinity/ic/actions/runs/25655953578

[dsarlis]

Run on f49d15b URL: https://github.com/dfinity/ic/actions/runs/25655953578

I noticed a failure for some system tests which seem to have failed due to:

failed to setup IC under test: Retried too many times: sending a request to Farm

and one which failed with

-- could not kill VM: TooManyRetries { message: "sending a request to Farm" }

so I would assume it's due to flakiness.

[github-actions]

Run on adcda17 URL: https://github.com/dfinity/ic/actions/runs/25661248563

[dsarlis]

@mraszyk Can you please retry this job? It seems there was some issue downloading certain dependencies...