Change keyboard level include guards to pragma once (#14248)

* Change keyboard level include guards to `pragma once`

And clean up a lot of layout macros

* Oops

* Remove dangling endif

keyboards/helix/local_drivers/serial.h

@@ -1,5 +1,4 @@
-#ifndef SOFT_SERIAL_H
-#define SOFT_SERIAL_H
+#pragma once
 
 #include <stdbool.h>
 
@@ -85,5 +84,3 @@ int  soft_serial_transaction(int sstd_index);
 #ifdef SERIAL_USE_MULTI_TRANSACTION
 int  soft_serial_get_and_clean_status(int sstd_index);
 #endif
-
-#endif /* SOFT_SERIAL_H */