staging: unisys: Remove unused driver

The visorchannel feature is rolled into visorbus now and its headers
are public under visorbus.h.  Remove the unused driver, the old
header file and all the ccflag includes in the Makefile.

Also remove VISORCHANNEL from all Kconfigs as it is not needed.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>