FIX: do not allow tag with name 'none' (PR #9867)

https://meta.discourse.org/t/none-tag-is-uneditable/152003

GitHub

We should be using sql here instead of using the AR models. It’s annoying because there are so many associations to delete… This case is so simple it might be ok.

I think it’s better if we iterate over the associations [:tag_users, :topic_tags, ... ] and delete the rows with sql. delete from #{table_name} where tag_id = :none_tag_id

Use sql in the migration instead of tag.destroy.

Update the migration to use SQL.