Update unused table list - consider moving to a `legacy` schema

> [!NOTE]
> Migrated from [augurlabs/augur#3425](https://github.com/augurlabs/augur/issues/3425)
> Originally opened by `@MoralCode` on 2025-11-20

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There appears to be a [docs page](https://oss-augur.readthedocs.io/en/main/schema/unused_data.html) listing unused tables.

I strongly suspect this is out of date.

I think its worth going through and auditing which tables are in use and sorting them into three buckets:
1. in use tables
2. unused tables we should keep for data preservation on older instances
3. unused tables that should be dropped

category 2 is what we should document in this page of the docs and potentially move over to a new schema

See also #141