[amp-story-interactive] Allow for not displaying results

## Describe the new feature or change to an existing feature you'd like to see

There are some cases for polls or quizes where the story publisher might not want to show the results. A simple case would be one of polling for customer satisfaction. If customers are not satisfied, the publisher might not want to show the results or make them public.

I think simply removing the response percentage text should do the trick, and having the visualisation similar to just one person having responded (100% for the selected option, 0% for all others)