Add migration to remove simple_captcha_data table
user
```ruby
class RemoveSimpleCaptchaData < ActiveRecord::Migration
  def up
    drop_table :simple_captcha_data
  end

  def down
    create_table :simple_captcha_data do |t|
      t.string :key, :limit => 40
      t.string :value, :limit => 6
      t.timestamps
    end

    add_index :simple_captcha_data, :key, :name => "idx_key"
  end
end
```
assistant