Here's what Todd said at the Google Group:
Sketchup.active_model.entities.erase_entities(page) should work, but
it hangs SketchUp. It's a known and reported bug.
To get around this bug, do this:
First, make the page you want to delete the active page. Then, issue
this from Ruby:
That means it can be done even if its a work around.
If not we could save the model prior to using the script and then saving it after, under another name or with a "_anim" after.
Not the best way but it would still mean we could render a smooth animation.