Your event is complimentary. You wish to delete payment method on your registration process.
On the Event Registration & Product Sales page - use Events -> Settings -> Advanced Settings -> Show Costs and set this field to No.
On the Pledge Participant Registration page - this page is designed for no cost registrations and no fees will be shown/charged.
For Registration Fees - The Payment Method option cannot be hidden or deleted from this 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 No Charge.