Cleanup Default Keymaps (#5442)

* Cleanup Default Keymaps to conform to QMK Firmware standards

* Minor fixes

* Revert some changes

keyboards/preonic/keymaps/default/config.h

@@ -1,7 +1,4 @@
-#ifndef CONFIG_USER_H
-#define CONFIG_USER_H
-
-#include "config_common.h"
+#pragma once
 
 #ifdef AUDIO_ENABLE
     #define STARTUP_SONG SONG(PREONIC_SOUND)
@@ -38,5 +35,3 @@
 
 /* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
 //#define MIDI_TONE_KEYCODE_OCTAVES 2
-
-#endif