vhost: vringh: Remove unused iotlb functions

The functions:
  vringh_abandon_iotlb()
  vringh_notify_disable_iotlb() and
  vringh_notify_enable_iotlb()

were added in 2020 by
commit 9ad9c49c ("vringh: IOTLB support")
but have remained unused.

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Message-Id: <20250617001838.114457-2-linux@treblig.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>