sxmo-common: move vim, mpv, and yt-dlp to pmb_recommends

Some users were complaining that they cannot uninstall vim. They may also want to uninstall mpv and yt-dlp (for vlc?) so we should allow them to.

Question: does _pmb_recommends only work on postmarketos-ui-* packages?

If so, we may have to make a sxmo-common-optional metapackage. Let me know the correct way to solve this.