LP1170861 Remove unused lineitem alert field

Remove extraneous field from the IDL field list for acq lineitem alerts.
The extra field prevented new alerts from getting saved.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Signed-off-by: Ben Shum <bshum@biblio.org>