Expiration of removed collection items and their associated artifacts does not work

On debusine.debian.net, the debian:suite collections have been configured to not retain removed collection items (full_history_retention_period and metadata_only_retention_period set to "0 days"), yet all the historical items are still present: https://debusine.debian.net/debian/base/collection/debian:suite/sid/

(The fact that the above web page claims "Always" for both retention period is tracked in #890 (closed) )

The debian:environments collection have been set with full_history_retention_period = 0 days and metadata_only_retention_period = 1 year. So all the historical items should no longer be linked to any artifact, but they still all have their associated artifacts: https://debusine.debian.net/debian/base/collection/debian:environments/freexian/search/?category=&name=&historical=on