removed function step_wait() from stepper.cpp

removed function step_wait() from stepper.cpp because its used nowhere.

Marlin/stepper.cpp

@@ -238,12 +238,6 @@ void st_wake_up() {
   ENABLE_STEPPER_DRIVER_INTERRUPT();
 }
 
-void step_wait(){
-    for(int8_t i=0; i < 6; i++){
-    }
-}
-
-
 FORCE_INLINE unsigned short calc_timer(unsigned short step_rate) {
   unsigned short timer;
   if(step_rate > MAX_STEP_FREQUENCY) step_rate = MAX_STEP_FREQUENCY;