Bug 14641: [SIGNED-OFF] Warns in subscription-add.pl

Bug 14641: [SIGNED-OFF] Warns in subscription-add.pl

Removes warn using Jonathan's suggestion!

To test:
1) Reproduce warns by clicking New Subscription
2) Apply patch
3) Click New Subscription again
4) Confirm warns are gone

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Patch removes the warn that come when clicking "New subscription"

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit fe7940257537042ff6ffab9c7b718e5b8a5dc368)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>