Event Contribution Invoice also sends to CC & BCC (privacy issue)

When I generate and send event contribution invoices by email, they also get send to the email adresses configured for the event as CC and BCC adresses.

I believe this is unwanted behaviour, as these CC & BCC adresses are mainly intended to inform people in an organisation of new registrations, whereas sending invoices for outstanding fees is a private matter and usually being handled by a finance coordinator within an organisaion.

The email invoices for event registrations should only be send to the event participant.

I have no clue where the code for this mechanism is to be found. If anyone can point me in the right direction, I am happy to work on submitting a PR for this.