For now, there's ~90% rows whose dictionary has a single `@context` key.
We should delete them.
When done, the following two queries should both return 0:
```
softwareheritage-indexer=> select count(*) from revision_intrinsic_metadata where metadata = '{"@context": https://doi.org/10.5063/schema/codemeta-2.0"}'::jsonb ;
count
--------
742428
(1 row)
softwareheritage-indexer=> select count(*) from origin_intrinsic_metadata where metadata = '{"@context": "https://doi.org/10.5063/schema/codemeta-2.0"}'::jsonb ;
count
--------
369096
(1 row)
```