Turning off the Popups in the Referral Program
To turn off the Referred Customer Welcome popup and Share Referral Link Popup (and the Create Account/Login Form #1 popup by extension), select the appropriate popup from the dropdown menu and click the "Customize Popup" button. These are the only two popups you would need to turn off to hide all referral program related popups.
You'll then see the option flip off your popup just below the text "Popup Enabled?".