Cleanup Default Keymaps (#5442)

* Cleanup Default Keymaps to conform to QMK Firmware standards

* Minor fixes

* Revert some changes

keyboards/subatomic/keymaps/default/config.h

@@ -1,7 +1,6 @@
-#ifndef CONFIG_USER_H
-#define CONFIG_USER_H
+#pragma once
 
-#include "../../config.h"
+// place overrides here
 
 /*
  * MIDI options
@@ -25,5 +24,3 @@
 
 /* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
 //#define MIDI_TONE_KEYCODE_OCTAVES 2
-
-#endif