Bug 26149: Remove jquery.checkboxes plugin from problem reports page

Bug 26149: Remove jquery.checkboxes plugin from problem reports page

This patch removes the inclusion of the jquery.checkboxes plugin from
the problem reports template in the staff interface.

To test, apply the patch and make sure the OPACReportProblem system
preference is enabled.

 - Submit a few OPAC problem reports if necessary
 - Go to Tools -> OPAC problem reports
 - Test that the "Select all" and "Clear all" controls at the top of the
   table work correctly.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>