iohelper: Remove unused mode
After 1eb6647979f8c nobody calls the iohelper with 6 arguments.
Everybody uses the other mode. Well, the only user of iohelper
after the previous commit is virFileWrapperFd really.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>