Keyboard: Refactor fourier to use split common code (#4582)

* Refactor fourier to use split common code

* Refactor fourier to use split common code - fix handedness when not using EE_HANDS or MASTER_LEFT

* add SOFT_SERIAL_PIN config

keyboards/fourier/keymaps/default/config.h

@@ -18,14 +18,8 @@ You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#ifndef CONFIG_USER_H
-#define CONFIG_USER_H
-
-#include "config_common.h"
+#pragma once
 
 /* Use I2C or Serial, not both */
-
 #define USE_SERIAL
 // #define USE_I2C
-
-#endif