Remove radius from SceneJS.Sphere

The radius property is not actually being used by the sphere node.

Its to subtly encourage optimal use. When you define a sphere of say, 20 bands and 30 slices, then the first time the sphere node is rendered it checks to see if a set of geometry buffers (ie. positions, uv, texture coords and indices) is currently loaded into VRAM, mapped by SceneJs to ID "sphere_20_30".

On the first time the sphere node is rendered, there are probably no such geometry buffers, so it creates, loads and binds them, then draws them.

Then when that sphere node is rendered again (or any other sphere node specifying 20 bands and 30 slices) then that buffer set will be found in VRAM and rendered again.

The sphere is always a unit sphere, to be sized if required using SceneJS.size nodes. That way the user is encouraged to re-use the same buffered geometry across various sized spheres. If you could vary the radius, then you might accidentally create hundreds of sphere geometry buffers.