[amp-story-player] Transitioning from one story to another affects the top page's history

[pshihn]

When the player transitions from one story to another, it adds a record to the top page's history. Causing the 'back' button to not work until n+1 clicks, where n is the number of story transitions.

This is because iframes affect the browser history. This could be avoided if inside the iframe, the location is changed using location.replace()

This seems really bad for UX on a page that uses the amp-story-player.

[gmajoulet]

Tracked here: #31010