More Bluetooth refactoring (#9905)

tmk_core/protocol/serial.h

@@ -35,13 +35,10 @@ ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.
 */
 
-#ifndef SERIAL_H
-#define SERIAL_H
+#pragma once
 
 /* host role */
 void    serial_init(void);
 uint8_t serial_recv(void);
 int16_t serial_recv2(void);
 void    serial_send(uint8_t data);
-
-#endif