Bug 20147: Allow translating prompt in label edit batch

Bug 20147: Allow translating prompt in label edit batch

Fix one untranslatable prompt in the label batch edit.

Test plan:

1) Go to Home -> Tools -> Label creator
2) Click on New -> Label batch
3) Add items to the batch
4) Select any of the items
5) Click on "Remove selected items"
6) Note the popup text
7) Apply patch, update a language, translate the msgid
   "Are you sure you want to remove label number(s): %s from this batch?"
8) Repeat 1-6. The popup text should now be translated.

Signed-off-by: Pasi Kallinen <pasi.kallinen@joensuu.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>