Expose delta_clip_start_height for use by others

Marlin/Marlin.h

                delta_segments_per_second,
                delta_diagonal_rod_trim_tower_1,
                delta_diagonal_rod_trim_tower_2,
-               delta_diagonal_rod_trim_tower_3;
+               delta_diagonal_rod_trim_tower_3,
+               delta_clip_start_height;
   void recalc_delta_settings(float radius, float diagonal_rod);
 #elif IS_SCARA
   void forward_kinematics_SCARA(const float &a, const float &b);