DELETE /entities/items/{item_id}/statements/{statement_id}/references/{reference_hash}
DELETE /entities/properties/{property_id}/statements/{statement_id}/references/{reference_hash}
DELETE /statements/{statement_id}/references/{reference_hash}

• optional metadata: tags, bot, comment.

How "Action API" does it: not exactly the same mechanism, but a similar outcome can be achieved with the wbremovereferences API module.