staging: unisys: visorbus: Remove unused struct in visorchannel.c

Removes struct safe_uis_queue, which is within struct visorchannel. The
struct is not used anywhere in the s-Par drivers.

Signed-off-by: David Binder <david.binder@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>