Piper 2 Dual Z Stepper Conversion Mod

This is a modification for the Z axis of the Piper 2. It retains the four lead screws (they are necessary for the gantry's overall stability) but forgoes two of the steppers, plus their associated hardware (Drivers, Couplers, etc). The two steppers can be easily driven in parallel by a single driver, eliminating the need for a CNC shield, reducing the overall complexity of the build. It also makes the gantry more stable, as each side is tethered and is more difficult to slide/skip when the motor