Drop old includes in serial.h

Marlin/src/core/serial.h

@@ -21,13 +21,8 @@
  */
 #pragma once
 
-//#include <stdint.h>
-
-//#include "../inc/MarlinConfigPre.h"
 #include "../HAL/HAL.h"
 
-// #include "../core/macros.h"
-
 /**
  * Define debug bit-masks
  */