staging: unisys: cleanup UNISYS_VISORUTIL

Commit 53490b54

 ("staging: unisys: move periodic_work.c into the
visorbus directory") removed the Kconfig option UNISYS_VISORUTIL, but
left one reference in a Kconfig select.  Remove this last reference.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>