update slides after review comments

[yannfeat]

@Crosita and @dgkf a few points deserve your attention:

• I removed the validation pipeline implementation slides altogether, as I think we already have enough slides without them, and that their interest is limited.
• I don't see what is wrong with the layout of the filters diagram on your screens. I checked on different web browsers, on different screens, tried rendering the presentations both locally and on GitHub pages, but the diagram renders fine for me. @dgkf could you please help me there?
• I think I will mention the reference image for the submissions WG for FDA submissions orally only.
• The icons that I added are from a free SVG repository: https://www.svgrepo.com/. The licences are either open source or public domain licences.