Use block cleaning instead of split flag

Marlin/src/module/planner.h

@@ -165,7 +165,6 @@ class Planner {
                  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