staging: unisys: vmcallinterface.h: Cleanup unused fields

With the simplified driver models we have more vmcalls that aren't
supported by linux guests.

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>