Bug 20302: Allow translating Delete button in Patron batch mod tool

Bug 20302: Allow translating Delete button in Patron batch mod tool

There is an untranslatable Delete-button in the patron batch modification
tool. Allow translating it.

Test plan:

1) Go to Home -> Tools -> Batch patron modification, put a patron's
   card number in the box, and click on Continue
2) At the bottom of the screen there is an drop-down entry for
   Attribute, click on the "New" at the nd of that line
3) There should now be another Attribute -line, with "Delete" -link
   at the end of that line
4) Apply patch, install a language
5) Repeat 1-3 in that language, the Delete-link should be shown in
   the correct language, if the msgid "Delete" was translated
   in xx-YY-staff-prog.po

Signed-off-by: Pasi Kallinen <pasi.kallinen@joensuu.fi>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>