Where did the MacPro 6,1 "Computer Sleep" setting go?
It is probable that Apple no longer feels the Computer sleep and Display sleep options are required.

The new Mac Pro has no spinning hard disk drives and has a modern power management system that can manage itself.

I suspect you can change settings using low level tools like pmset, but that those settings will be ignored.

Staying Awake

To keep your Mac awake during long running processes, use the Terminal.app command caffeinate:

caffeinate