Fix compiler warning: variable 'previous_millis_cmd' set but not used

Firmware/ultralcd.cpp

@@ -3518,7 +3518,6 @@ bool lcd_calibrate_z_end_stop_manual(bool only_z)
 
     // Until confirmed by the confirmation dialog.
     for (;;) {
-        unsigned long previous_millis_cmd = _millis();
         const char   *msg                 = only_z ? _i("Calibrating Z. Rotate the knob to move the Z carriage up to the end stoppers. Click when done.") : _i("Calibrating XYZ. Rotate the knob to move the Z carriage up to the end stoppers. Click when done.");////MSG_MOVE_CARRIAGE_TO_THE_TOP c=20 r=8////MSG_MOVE_CARRIAGE_TO_THE_TOP_Z c=20 r=8
         const char   *msg_next            = lcd_display_message_fullscreen_P(msg);
         const bool    multi_screen        = msg_next != NULL;
@@ -3527,13 +3526,10 @@ bool lcd_calibrate_z_end_stop_manual(bool only_z)
         lcd_encoder_diff = 0;
         lcd_encoder = 0;
         for (;;) {
-//          if (_millis() - previous_millis_cmd > LCD_TIMEOUT_TO_STATUS)
-//             goto canceled;
             manage_heater();
             manage_inactivity(true);
             if (abs(lcd_encoder_diff) >= ENCODER_PULSES_PER_STEP) {
                 _delay(50);
-                previous_millis_cmd = _millis();
                 lcd_encoder += abs(lcd_encoder_diff / ENCODER_PULSES_PER_STEP);
                 lcd_encoder_diff = 0;
                 if (! planner_queue_full()) {