xfs: remove dead ENODEV handling in xfs_destroy_ioend

No driver returns ENODEV from it bio completion handler, not has this
ever been documented.  Remove the dead code dealing with it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>