ledger: add StateProofID to AccountData.ClearOnlineState()

[cce]

Summary

Clear out AccountData.StateProofID when ClearOnlineState() is called, by resetExpiredOnlineAccountsParticipationKeys (as part of #2924)

Test Plan

Updated TestExpiredAccountGeneration to generate random online account data, so that it fails without this change.

[tsachiherman]

looks good.

[tsachiherman]

while I do agree with this change, we can't implement it like this.

[tsachiherman]

I think that this should be implemented with a future flag. Then, we'll be able to merge it to master.

[pzbitskiy]

I think we need a hotfix into betanet

[id-ms]

I would suggest we move those fields into a new struct and clean the entire struct.
clearing individual fields will lead to errors (as we have seen)

confirmed we're going to hot fix.

[cce]

@algoidan we've already moved the fields into a VotingData{} struct on the feature/unlimited-assets branch, and I just made the change you suggested to clear the entire struct here: a5e867f