Bug 29794: Add missing include in delete_items.pl

Bug 29794: Add missing include in delete_items.pl

This patch adds a missing include so the script is no longer broken.

To test:
1. Choose an item that is checked out and copy its barcode
2. Run:
   $ kshell
  k$ perl misc/cronjobs/delete_items.pl --verbose \
          --where "barcode='39999000010831'"
=> FAIL: It explodes with:
Can't locate object method "find" via package "Koha::Items"...
3. Apply this patch
4. Repeat 2
=> SUCCESS: You get:
Where statement:  where barcode='39999000010831'
Item '549' not deleted: book_on_loan
5. Sign off :-D

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>