staging: unisys: visorbus: Remove unused functions

Remove visorbus_clear_channel, visorchannel_signalqueue_slots_avail,
visorchannel_signalqueue_max_slots, visorchannel_clear, and
visorchannel_debug which are no longer called by any driver.

Signed-off-by: Bryan Thompson <bryan.thompson@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <Timothy.Sell@unisys.com>
Acked-By: Neil Horman <nhorman@tuxdriver.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>