s390/vfio-ap: Remove gmap_convert_to_secure() from vfio_ap_ops

s390/vfio-ap: Remove gmap_convert_to_secure() from vfio_ap_ops

If the page has been exported, do not re-import it. Imports should
only be triggered by the guest. The guest will import the page
automatically when it will need it again, there is no advantage in
importing it manually.

Moreover, vfio_pin_pages() will take an extra reference on the page and
thus will cause the import to always fail. The extra reference would be
dropped only after pointlessly trying to import the page.

Fixes: f88fb1335733 ("s390/vfio-ap: make sure nib is shared")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Link: https://lore.kernel.org/r/20241115135611.87836-1-imbrenda@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>