wan: remove sbni/granch driver

The driver was merged in 1999 and has only ever seen treewide cleanups
since then, with no indication whatsoever that anyone has actually
had access to hardware for testing the patches.

>From the information in the link below, it appears that the hardware
is for some leased line system in Russia that has since been
discontinued, and useless without any remote end to connect to.

As the driver still feels like a Linux-2.2 era artifact today, it
appears that the best way forward is to just delete it.

Link: https://www.tms.ru/%D0%90%D0%B4%D0%B0%D0%BF%D1%82%D0%B5%D1%80_%D0%B4%D0%BB%D1%8F_%D0%B2%D1%8B%D0%B4%D0%B5%D0%BB%D0%B5%D0%BD%D0%BD%D1%8B%D1%85_%D0%BB%D0%B8%D0%BD%D0%B8%D0%B9_Granch_SBNI12-10


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>