Deprecate SET_EXTRUDER_STEP_DISTANCE and SYNC_STEPPER_TO_EXTRUDER.
Recommend using SET_EXTRUDER_ROTATION_DISTANCE and
SYNC_EXTRUDER_MOTION.
Deprecate the extruder "shared_heater" option and reocmmend using
extruder_stepper config sections to obtain the same functionality.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>