Your event is complimentary. You wish to delete payment method on your registration process.
On the No Cost Pledge Participant Registration page - this page is designed for no cost registrations and no fees will be shown or charged.
If you are using either the Registration & Product Sales or the Registration Fees page - The Payment Method option cannot be hidden or deleted from the registration page. However, if your event is complementary, make sure to check the 'No Charge' option under Tools -> Payment Settings. This way, the Payment Method box will show the No Charge option.