storage.postgresql: Use origin_visit_status.type value as source

This stops using the origin_visit.type as fallback values as now, the database has been migrated.

So this makes the origin_visit_status.type a not nullable column.

This also drops now redundant join instructions on origin_visit table when reading.

Related to swh/infra/sysadm-environment#2968 (closed)

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Migrated from D5019 (view on Phabricator)