You can't disable it because it's a core part of the system. It's the calendar service of the phone and closely connected to the clock. Force disabling it will brick the phone actually.
My suggestion, just turn it back on. It's not going to cause problems, it will just stay in the background. It will not cause any notification if there's nothing scheduled in the first place, and disabling it's notifications or whatever will not save you battery or space on the phone anyway.