can: remove obsolete empty ioctl() handler

With commit c7cbdbf2 ("net: rework SIOCGSTAMP ioctl handling") the only
ioctl function in can_ioctl() has been removed.

As this SIOCGSTAMP ioctl command is now handled in net/socket.c we can entirely
remove the CAN specific ioctl functions.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>