staging: Also remove the Unisys visorbus.h

The commit that removed the Unisys s-Par and visorbus drivers
left around the include/linux/visorbus.h file mentioned in the
MAINTAINERS entry, we can also remove that too.

Fixes: e5f45b01

 ("staging: Remove the drivers for the Unisys s-Par")
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Link: https://lore.kernel.org/r/20220606132200.2873243-1-pbrobinson@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>