Drop book 2 scene 7 (cornell_balls)?

[hollasch]

I don't know what this scene's doing in the book 2 main function; perhaps it's supposed to be an intermediate step to the cornell_smoke scene. It includes the following constant_medium sphere:

auto boundary = make_shared<sphere>(point3(160,100,145), 100, make_shared<dielectric>(1.5));
objects.add(boundary);
objects.add(make_shared<constant_medium>(boundary, 0.1, color(1,1,1)));

Here's the resulting image:

It's not mentioned in the text. Should we drop it?

[hollasch]

Decided to drop this. See #653.