It appears the Jobs table was removed in 8adb433e3b48638f3faaecc61ae5cb63efefff6e, but the Jobsets schema was never updated to reflect this. This relationship was added in efa1f1d4fbdc468c61f7403e8709d0295e052c7f, roughly 3 months prior.

Previously, one would see a message similar to the following logged when deleting a jobset:

17:38:23 hydra-server.1       | DBIx::Class::Relationship::CascadeActions::delete(): Skipping cascade delete on relationship 'jobs' - related resultsource 'Hydra::Schema::Jobs' is not registered with this schema at /home/vin/workspace/vcs/hydra/src/script/../lib/Hydra/Controller/Jobset.pm line 106