To hide registration buttons on your event page, all you need to do is update your Registration settings on your Event's Dashboard.
Go to 'Setup > Registration' in the left-hand panel.
Click on the ADVANCED tab
Scroll down to the "Enable/Disable Registration" section and uncheck the checkbox next to "Registration is Active."
Once unselected, click "Update."
When you go back to your event page, if an attendee clicks on any of the RSVP buttons, it will say your registration is closed:
Want to turn registration back on?
Just go back to the same spot, check "Registration is Active," hit Update, and the button will be active again.