Bug 28152: Log the "duplicate item barcode" error

Bug 28152: Log the "duplicate item barcode" error

Looking at the code this 'import_error' column is empty for the last 9 years. Not sure it makes much sense to have this single error now.

commit 1dba9c6409d78cb1f90de6c1300cb5b63fb1b851
Date:   Wed Oct 10 14:21:22 2012 -0500
    Bug 7131: teach MARC import how to overlay items

Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>