staging: slicoss: remove the staging driver

A "real" driver for this hardware has now landed in the networking tree,
so remove this old staging driver so that we don't have multiple drivers
for the same hardware, and so people don't waste their time trying to
clean up this old code.

Cc: Lior Dotan <liodot@gmail.com>
Cc: Christopher Harrer <charrer@alacritech.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>