Use block cleaning instead of split flag

Marlin/src/module/motion.cpp

     saved_feedrate_percentage = feedrate_percentage;
     feedrate_percentage = 100;
     gcode.refresh_cmd_timeout();
-    planner.split_first_move = false;
   }
   else {
     feedrate_mm_s = saved_feedrate_mm_s;
     feedrate_percentage = saved_feedrate_percentage;
     gcode.refresh_cmd_timeout();
-    planner.split_first_move = true;
   }
 }
 

Marlin/src/module/planner.cpp

   uint8_t Planner::last_extruder = 0;     // Respond to extruder change
 #endif
 
-bool Planner::split_first_move = true;
-
 int16_t Planner::flow_percentage[EXTRUDERS] = ARRAY_BY_EXTRUDERS1(100); // Extrusion factor for each extruder
 
 float Planner::e_factor[EXTRUDERS],               // The flow percentage and volumetric multiplier combine to scale E movement
     position[E_AXIS] = target[E_AXIS];
 
   // Always split the first move into two (if not homing or probing)
-  if (!blocks_queued() && split_first_move) {
+  if (!blocks_queued()) {
     #define _BETWEEN(A) (position[A##_AXIS] + target[A##_AXIS]) >> 1
     const int32_t between[XYZE] = { _BETWEEN(X), _BETWEEN(Y), _BETWEEN(Z), _BETWEEN(E) };
     DISABLE_STEPPER_DRIVER_INTERRUPT();

Marlin/src/module/planner.h

                  travel_acceleration,  // Travel acceleration mm/s^2  DEFAULT ACCELERATION for all NON printing moves. M204 MXXXX
                  max_jerk[XYZE],       // The largest speed change requiring no acceleration
                  min_travel_feedrate_mm_s;
-    static bool split_first_move;
 
     #if HAS_LEVELING
       static bool leveling_active;          // Flag that bed leveling is enabled

Marlin/src/module/stepper.cpp

   #endif // !COREXY && !COREXZ && !COREYZ
 
   kill_current_block();
+  cleaning_buffer_counter = -(BLOCK_BUFFER_SIZE - 1); // Ignore remaining blocks
 }
 
 void Stepper::report_positions() {