Bug 21849: Two useless Koha::Account::Offset->new calls need attention

Bug 21849: Two useless Koha::Account::Offset->new calls need attention

Came across those calls in bug 20598 in _FixOverduesOnReturn

        Koha::Account::Offset->new(
            {
                debit_id => $accountline->id,
                type => 'Forgiven',
                amount => $amountoutstanding * -1,
            }
        );

This does nothing if you don't store data.

Test Plan:
1) Apply this patch
2) Set up 2 items with overdue fines
3) Return one with dropbox mode
4) Note the dropbox account offset is created
5) Return one with full fine forgiveness
6) Note the forgiven account offset is created

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>