staging: remove sbe-2t3e3 driver.

It never really got cleaned up properly, and no one is working on it, so
remove it.  If someone wants to pick it up, this can be easily reverted.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>