No more Flatpak (by default) in Ubuntu Flavors

The Ubuntu Flavors
offerings (Kubuntu and the like) have decided
that the way to improve the user experience is to put more emphasis on the
Snap package format.

Going forward, the Flatpak package as well as the packages to
integrate Flatpak into the respective software center will no
longer be installed by default in the next release due in April
2023, Lunar Lobster. Users who have used Flatpak will not be
affected on upgrade, as flavors are including a special migration
that takes this into account. Those who haven’t interacted with
Flatpak will be presented with software from the Ubuntu
repositories and the Snap Store.