capi: Perform scheduled capifs removal

udev fully replaces this special file system that only contains CAPI
NCCI TTY device nodes. User space (pppdcapiplugin) works without
noticing the difference.

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