CAPI: Schedule capifs for removal

With dynamic TTY nodes and the help of udev, we no longer need this
special filesystem. Schedule it for removal in one year from now.

As a last duty to this feature, move its help to right option so that
users can read the rationale.

Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>