Broken Web Stories Demo

## 🐛 Bug Report

### Current behavior

The [Stories in AMP](https://amp.dev/documentation/examples/introduction/stories_in_amp/) page has a "View demo" link that used to work.

But now it embeds `http://localhost:8084/documentation/examples/introduction/stories_in_amp` in an iframe which of course doesn't work.

The correct link is https://preview.amp.dev/documentation/examples/introduction/stories_in_amp, however that page also points to some resources on `localhost:8080` which is incorrect.

- Page link: https://amp.dev/documentation/examples/introduction/stories_in_amp/

### Expected behavior/code

The demo should work

### Reproduction procedure

1. Visit https://amp.dev/documentation/examples/introduction/stories_in_amp/ or https://preview.amp.dev/documentation/examples/introduction/stories_in_amp and see the broken demo with invalid AMP

- What browser are you using? Chrome
- What O/S are you using? macOS