I'm afraid we can't remove that box from the screen it appears on, although not every checkout process requires the opt-in message. PayPal's standard service will add everyone to your list, for example. But on our free checkout page and the credit card checkout page which connects to Auth.net, 2CO or Paypal's expanded services the opt-in box is a requirement.
If you aren't using PayPal Standard to handle your pre-orders then I would recommend reminding your buyers to check the box during checkout so that they are added to your internal mailing list for the update. Even if they don't their information and email address will still get recorded in your sales records so that there's a way to verify their purchase if they forget to opt-in.