Remove all previous ways of linking things. part of OBE-105
user
```ruby
class RemoveLinksThroughHasMany < ActiveRecord::Migration
  def self.up
    drop_table "script_lists"
    drop_table "survey_lists"
    drop_table "survey_to_script_lists"
    drop_table "script_to_script_links"
    drop_table "extract_to_extract_links"
    drop_table "extract_to_extract_lists"
  end

  def self.down
  end
end
```
assistant