Revert implementation of motor delay in method step

Motor delay must support multitasking. See:
https://www.arduino.cc/en/Tutorial/BlinkWithoutDelay

libraries/Stepper/src/Stepper.cpp

@@ -153,7 +153,12 @@ void Stepper::step(int steps_to_move)
   // decrement the number of steps, moving one step each time:
   while (steps_left > 0)
   {
-    delayMicroseconds(this->step_delay);  // move only if the appropriate delay has passed
+    unsigned long now = micros();
+    // move only if the appropriate delay has passed:
+    if (now - this->last_step_time >= this->step_delay)
+    {
+      // get the timeStamp of when you stepped:
+      this->last_step_time = now;
       // increment or decrement the step number,
       // depending on direction:
       if (steps_to_move >= 0)
@@ -174,6 +179,7 @@ void Stepper::step(int steps_to_move)
       stepMotor(this->step_number % phase_count);
       // decrement the steps left:
       steps_left--;
+    }
   }
 }
 

libraries/Stepper/src/Stepper.h

@@ -156,6 +156,7 @@ class Stepper {
 
     // motor pin numbers:
     unsigned char motor_pin[5];   // Maximum 5 control signals
+    unsigned long last_step_time; // time stamp in us of when the last step was taken
 };
 
 #endif