Fix skybox render-world cleanup on component removal (#24389)

# Objective

When `Skybox` was moved to `bevy_light` (#22682), extraction moved from
`ExtractComponentPlugin` to a manual extraction implementation due to
orphan rules. In the process, the functionality of `SyncComponentPlugin`
was lost because it is no longer added automatically.

This manifests as the extracted skybox sticking around in the render
world even after removing `Skybox` from the camera.

## Solution

Register `SyncComponentPlugin` manually for `Skybox`.
 
## Testing
 
- Reproduced with `cargo run --example anisotropy --features="jpeg
pbr_anisotropy_texture"`.
- Press `Space` until the example switches from environment map mode
back to directional light mode.
- The skybox now disappears correctly.

Co-authored-by: Dahmen issam <issam.dahmen@fittingbox.com>