Bug 37152: Deleting patron categories doesn't warn about categories in use

Bug 37152: Deleting patron categories doesn't warn about categories in use

You can't delete a patron category when it is in use, but because the
script which handles delete confirmation is expecting the wrong op,
cud-delete_confirm rather than delete_confirm, you don't get any warning,
just a failure to delete error message.

Test plan:
 1. Without the patch, Administration - Patron categories
 2. On the row for Staff, click Delete, Delete this category
 3. Note an error message telling you to check the logs for details
 4. Apply patch, restart_all
 5. With the patch, repeat steps 1-2, note that instead of a button for
    Delete this category you get a warning that it is in use
 6. In the list of categories, row for Board, click Delete, Delete this category
 7. Note that the (unused) Board category was deleted

Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>