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

[MoralCode]

There appears to be a docs page 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I strongly suspect this is out of date.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 #3423

[SatyamKumarCS]

Hi! I'd like to take this up. I can go through the existing tables, classify them into the three categories you mentioned, and update the docs accordingly. Could you please assign this issue to me?

Thanks!

[MoralCode]

While you are free to take a shot at this issue, I strongly suspect this is the kind of task that is best done by a core maintainer who is familiar with the history of each table and whether or not there may be instances using them.