Zero Value Contributions shouldn't generate a transaction to batch

When a participant registers for an event using a zero value option in a priceset, the system generates a zero value contribution record and a corresponding transaction that then becomes available to batch.

It would be better if these zero event registrations didn't generate a zero value contribution at all or at least didn't generate a transaction that then needs to be batched. This is confusing for the user who's batching because the transaction shows up as affecting their cash account but it's a zero value entry so it shouldn't be there in the first place.