Now that the kinematic classes call the mcu_stepper with millimeters
and seconds it is no longer necessary for them to directly access the
stepper's position in absolute steps. Rename
mcu_stepper.commanded_position to mcu_stepper._commanded_pos to make
clear it is not a variable intended to be externally accessed.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>