Bug 24776: Remove Borrowers.IsDebarred call

Bug 24776: Remove Borrowers.IsDebarred call

Borrowers Template Toolkit plugin contains method IsDebarred that can be directly called from Koha::Patron object.

Also in template circ/returns.tt, when patron is restricted and checkin was backdated, var "patron" is undefined, should be "issue.patron".

Test plan :
1) Enable system preference SpecifyReturnDate
2) For a patron without restriction create a checkout
3) Create a manual restriction to debarre patron
4) Go to return page and click on "Checkin settings"
5) Specify a date in the past, barcode and click "Check in"
6) You see message "Jon Doe is restricted. Please verify this patron should still be restricted."

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>