Remove requests to 'idx_storage.content_language_get'.
It's broken since swh.indexer.storage v0.3.0, as it now returns attr objects instead of dicts: https://sentry.softwareheritage.org/share/issue/892044828a09460cab28283afc926cde/
And it wasn't very useful anyway (it barely contains results for any content), so I'm removing this code entirely.
Half-resolves #2729 (closed)
Migrated from D4353 (view on Phabricator)