Bug 29116: Use a pre-existing accessor instead of reimplementing it

Bug 29116: Use a pre-existing accessor instead of reimplementing it

We can use the Koha::Patron::is_expired accessor instead of re-writing
it in request.pl.

To test:
 1) Make that a warning is being shown with and without this patch
    when placing a hold to an expired patron account

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>