Bug 6530: Item Due notice label displaying as 'unknown'

Bug 6530: Item Due notice label displaying as 'unknown'

Some of the translated sql files still had 'Item_DUE' instead
of 'Item_Due' causing the staff interface to display 'unknown'
instead of the correct description.

To test:
- Do a new installation, using German, French, Polish, Russian or Ukrainian sample files.
- Actived EnhancedMessagingPreferences
- Create a new patron category and check message descriptions display correctly

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>