Db cleanup

[briri]

Fixes #2818

Changes proposed in this PR:

• See ticket for specific columns and tables that were removed.
• Updated code to remove references

Exceptions:

• Did not remove the settings table. We fixed a bug with the exported_plans table so I think it is still used. Not sure why we would want to retain the selected font and margins but 🤷🏻‍♂️
• See the maDMP PR migration for the removal of columns from research_outputs and removing the mime_types table

[raycarrick-ed]

@briri I think we need to discuss this. Maybe on Monday?

Most of this looks fine from what I can tell but I am concerned about the use of "is_other" and "other_organisation" because I think we may be using these differently from you. At least, specifically:
Org.where(is_other: true)
and
Org.where(managed: false)
are not the same things.
We have a single "Other" org still which is managed and we have users who have org = other and then some value in the other_organisation field.

Let's talk about it Monday. Cheers.

[briri]

ok @raycarrick-ed if those two fields are still used heavily in your installations then I can revert those. The switch over from is_other to managed was part of the move to use the ROR API which I know has been problematic.

Happy to chat about it more on Monday.