Bug 15228: Patron card batches - Improve translatability

 Bug 15228: Patron card batches - Improve translatability

This patch removes the \n\n from a translatable string
as those don't translate correctly to new lines.

It also switches 'item' for 'patron' to avoid confusion
with catalog items.

To test:
1) Trigger changed error message
- Create a new batch with 1 patron entry
- Select patron in list using the checkbox
- Click 'Remove selected patrons' in toolbar
- Verify alert displays correctly

2) Verify that the page no longer uses "items" but
   patrons instead.

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as advertised

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>