Move serialization format thing closer to the other one

[rparrett]

It seems that most of the changes suggested by the current guide for #5473 are not necessary after #5723.

I think the other section on serialization covers the rest, so I believe we can just delete this one.

Here's what I actually see when serializing ScalingMode with 0.8 and bevy main

// 0.8
{
    "type": "bevy_render::camera::projection::ScalingMode",
    "value": FixedHorizontal(720.0),
}

// bevy main
{
    "bevy_render::camera::projection::ScalingMode": FixedHorizontal(720.0),
}