vhost: vringh: Remove unused functions

The functions:
  vringh_abandon_kern()
  vringh_abandon_user()
  vringh_iov_pull_kern() and
  vringh_iov_push_kern()
were all added in 2013 by
commit f87d0fbb ("vringh: host-side implementation of virtio rings.")
but have remained unused.

Remove them and the two helper functions they used.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Message-Id: <20250617001838.114457-3-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>
Reviewed-by: Simon Horman <horms@kernel.org>