storage.db: Drop db.origin_visit_upsert behavior
The initial desired behavior was to allow creation of origin-visit if they already had their id set. This is the what's needed for the replayer to actually work.
But somehow, this left the possibility to update the origin-visit... This commit fixes it by dropping conflictual origin-visits if any. In effect, we can no longer overwrite origin-visits (pg-storage wise).
Related to T2310
Test Plan
tox
Migrated from D3416 (view on Phabricator)