can: slcan: remove useless header inclusions

Include only the necessary headers.
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Link: https://lore.kernel.org/all/20220728070254.267974-3-dario.binacchi@amarulasolutions.comSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/slcan/slcan-core.c

@@ -48,9 +48,6 @@
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>
 #include <linux/rtnetlink.h>
-#include <linux/if_arp.h>
-#include <linux/if_ether.h>
-#include <linux/sched.h>
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/kernel.h>