Remove the introductionary comments from `query_jobs.sql` and
`query_workers.sql`. Sqlc got confused by this, and placed them in the
wrong (well, not-intended-by-me) place in the generated Go code.
No functional changes.
This is a bit more work than other queries, as it also breaks apart the
fetching of the job and the worker into separate ones. In other words,
internally the persistence layer API changes.
