pbio/serial: drop linux includes
These are not used by pbio, only by pbdrv.
// Copyright (c) 2019 Laurens Valk
// Copyright (c) 2019 LEGO System A/S
-#include <fcntl.h>
-#include <errno.h>
-#include <sys/ioctl.h>
-#include <termios.h>
-#include <unistd.h>
-
#include <pbio/port.h>
#include <pbdrv/config.h>
#include <pbio/error.h>
