remove additional email fields on review page

My first thought is we don't need `additional_email_address` because the form never submits them. So I thought of:
```ruby
def email_addresses
  params[:confirmation_email][:email_addresses].reject(&:blank?)
end
```
But will `params[:confirmation_email][:email_addresses]` ever contain blank values, or is it only `params[:confirmation_email][:additional_email_address]` that would have blank values (the text inputs)?

If that is the case we can do away with this method altogether? We can revert this commit to bring it back when we want to. Github has even introduced a handy UI for us to do this! (https://github.com/blog/1857-introducing-the-revert-button)