Bug 30708: Do not allow edition of 'status for item added to train'

Bug 30708: Do not allow edition of 'status for item added to train'

It does not seem useful to enforce it at lower level, it is not a
condition that will break the feature, but it does not feel correct to
allow the modification of this value

Sponsored-by: BULAC - http://www.bulac.fr/
Signed-off-by: BULAC - http://www.bulac.fr/
Signed-off-by: Heather Hernandez <heather_hernandez@nps.gov>
Signed-off-by: Laurence Rault <laurence.rault@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>