Staging: ipack/bridges/tpci200: remove tpci200_slot_unregister

It is not needed as the IP module should free its IRQ using
tpci200_free_irq callback.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>