Examples: Fix webgl_buffergeometry_instancing_lambert.

[Mugen87]

Fixed #18801.

[mrdoob]

Thanks!

[mrdoob]

Hmm...

@WestLangley I think this example is confusing now as there is a simpler way to do this (just use InstancedMesh). Do you think it is still needed?

[WestLangley]

I promoted it because it shows how to hack an existing shader, and perhaps more importantly, a custom depth shader.

I also promoted it because it avoids using String.replace() to inject code snippets. This approach is more-easily readable.

Those were the original reasons, but I do not mind if you remove the example.

[mrdoob]

Right.
Maybe we should modify it a bit so it doesn't something that can't be done with InstancedMesh alone.

[WestLangley]

I filed a PR to remove it so as not to compete with the newer InstancedMesh feature.