excalibur: Stop expired scans from being reparsed every tick.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit 134d9e50c6f979ba59a2aba77672fbfc4ccdda18)
excalibur: Stop parser error message being raised whenever there are expired unparsed scans in the database.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit b9a9a9470d18241f4ee0a35bd8c4bd86d7cd55d0)