General cleanup around high level move functions

- Use new `DEBUG_POS` macro for `DELTA` debug
- Neaten up `prepare_move` a smidgen
- Remove an old commented `prepare_move()` line

Marlin/Marlin_main.cpp

@@ -2343,7 +2343,6 @@ static void homeaxis(AxisEnum axis) {
         #else
           sync_plan_position();
         #endif
-        //prepare_move();
       }
 
       feedrate = retract_recover_feedrate * 60;
@@ -7322,12 +7321,8 @@ void mesh_plan_buffer_line(float x, float y, float z, const float e, float feed_
         adjust_delta(target);
       #endif
 
-      //SERIAL_ECHOPGM("target[X_AXIS]="); SERIAL_ECHOLN(target[X_AXIS]);
-      //SERIAL_ECHOPGM("target[Y_AXIS]="); SERIAL_ECHOLN(target[Y_AXIS]);
-      //SERIAL_ECHOPGM("target[Z_AXIS]="); SERIAL_ECHOLN(target[Z_AXIS]);
-      //SERIAL_ECHOPGM("delta[X_AXIS]="); SERIAL_ECHOLN(delta[X_AXIS]);
-      //SERIAL_ECHOPGM("delta[Y_AXIS]="); SERIAL_ECHOLN(delta[Y_AXIS]);
-      //SERIAL_ECHOPGM("delta[Z_AXIS]="); SERIAL_ECHOLN(delta[Z_AXIS]);
+      //DEBUG_POS("prepare_move_delta", target);
+      //DEBUG_POS("prepare_move_delta", delta);
 
       plan_buffer_line(delta[X_AXIS], delta[Y_AXIS], delta[Z_AXIS], target[E_AXIS], feedrate / 60 * feedrate_multiplier / 100.0, active_extruder);
     }
@@ -7417,13 +7412,10 @@ void prepare_move() {
     if (!prepare_move_scara(destination)) return;
   #elif ENABLED(DELTA)
     if (!prepare_move_delta(destination)) return;
-  #endif
-
-  #if ENABLED(DUAL_X_CARRIAGE)
-    if (!prepare_move_dual_x_carriage()) return;
-  #endif
-
-  #if DISABLED(DELTA) && DISABLED(SCARA)
+  #else
+    #if ENABLED(DUAL_X_CARRIAGE)
+      if (!prepare_move_dual_x_carriage()) return;
+    #endif
     if (!prepare_move_cartesian()) return;
   #endif