staging: unisys: Remove visorchannel stub

Visorchannel directory has been stripped down to almost nothing, and is
no longer referenced. This finishes getting rid of the directory.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>