[Example] Slow page loading on WebNN + OpenCV.js pages

[ibelem]

The page loading is slow for WebNN and OpenCV.js combined pages like https://intel.github.io/webml-polyfill/examples/image_classification/. I don't think we need to download webml-polyfill for OpenCV example, and we don't need to download opencv relevant js for WebNN.

Let's think about the fast page loading for end users and mobile users.