example render_to_texture: remove extra light (#13398)

# Objective

- in example `render_to_texture`, #13317 changed the comment on the
existing light saying lights don't work on multiple layers, then add a
light on multiple layers explaining that it will work. it's confusing

## Solution

- Keep the original light, with the updated comment

## Testing

- Run example `render_to_texture`, lighting is correct

examples/3d/render_to_texture.rs

@@ -85,14 +85,16 @@ fn setup(
  first_pass_layer.clone(),
  ));
 
- // Light for the first pass
- // NOTE: Lights only work properly when in one render layer.
+ // Light
+ // NOTE: we add the light to both layers so it affects both the rendered-to-texture cube, and the cube on which we display the texture
+ // Setting the layer to RenderLayers::layer(0) would cause the main view to be lit, but the rendered-to-texture cube to be unlit.
+ // Setting the layer to RenderLayers::layer(1) would cause the rendered-to-texture cube to be lit, but the main view to be unlit.
  commands.spawn((
  PointLightBundle {
  transform: Transform::from_translation(Vec3::new(0.0, 0.0, 10.0)),
  ..default()
  },
- first_pass_layer.clone(),
+ RenderLayers::layer(0).with(1),
  ));
 
  commands.spawn((
@@ -134,17 +136,6 @@ fn setup(
  MainPassCube,
  ));
 
- // Light
- // NOTE: we add the light to both layers so it affects both the rendered-to-texture cube, and the cube on which we display the texture
- // Setting the layer to RenderLayers::layer(0) would cause the main view to be lit, but the rendered-to-texture cube to be unlit.
- // Setting the layer to RenderLayers::layer(1) would cause the rendered-to-texture cube to be lit, but the main view to be unlit.
- commands.spawn((
- PointLightBundle {
- transform: Transform::from_translation(Vec3::new(0.0, 0.0, 10.0)),
- ..default()
- },
- RenderLayers::layer(0).with(1),
- ));
  // The main pass camera.
  commands.spawn(Camera3dBundle {
  transform: Transform::from_xyz(0.0, 0.0, 15.0).looking_at(Vec3::ZERO, Vec3::Y),