No more Flatpak (by default) in Ubuntu Flavors

The Ubuntu Flavorsofferings (Kubuntu and the like) have decidedthat the way to improve the user experience is to put more emphasis on theSnap package format.

Going forward, the Flatpak package as well as the packages tointegrate Flatpak into the respective software center will nolonger be installed by default in the next release due in April2023, Lunar Lobster. Users who have used Flatpak will not beaffected on upgrade, as flavors are including a special migrationthat takes this into account. Those who haven't interacted withFlatpak will be presented with software from the Ubunturepositories and the Snap Store.