OnStep minPCB 4

A simplified version of maxpcb4 board from hdutton without drivers or power regulators, power is supplied either via usb or jp1 and steppers are driven by external closed loop drivers like these.

This better matches my use case which does not require st4 and relies on pulse guiding from phd2 and an intel nuc. Reducing complexity reduces failure modes and headaches when I just want to image. Because there are no drivers on board a 24/12v power supply is not needed and because I do not rely on the focuser/rotator axis they were omitted as well.