If you don’t want to turn off a Calendar Overlay and instead remove it entirely from your Calendar, you can use the Overlays management dialog to do so.

There are several options of Source Calendars to use as an Overlay. This includes calendars provided by Keep&Share, any calendars you create in your account, any calendars shared with you, and more. As a result, removing a Calendar Overlay does not delete the source Calendar from your account. Any source Calendar will always be available in your account, even after you remove it as a Calendar Overlay. You can always go back and add the Calendar Overlay to your Calendar again.

How to remove a Calendar Overlay from your Calendar