(Bug1353802) Don't call delete_records for new artefacts.

In ArtefactType::commit, don't bother calling delete_records
if we know the artefact that is being committed is new. In
testing the addition 2000 users from a CSV file, this patch
shaved 4 seconds off the completion time.

Change-Id: I5b22cb5fc936e67e9a37a0022a4488fc30604d03
Signed-off-by: Nigel Cunningham <nigelc@catalyst-au.net>
Merge "(Bug1353802) Don't call delete_records for new artefacts."