Is Image Noise Removal Image Enhancement or Image Restoration Operation?
It depends on the final goal and the model used.
If we assume we have an image - $ I $ which is a result of a sum on of an image $ W $ with noise $ n $: $I = W + n$ and our goal by reducing the noise is estimating $ W $ than this process is restoration.
Yet I could try achieving a different goal by denoising, such as making it look better (Subjective target) or use prior such as Piecewise Constant image which means the denoising process if more of an enhancement to the image.