installation: Remove no longer needed ostree version checks
installation: Remove no longer needed ostree version checks

Flatpak depends on ostree 2018.9, so there's no need for these checks
any more.

Closes: #2704
Approved by: alexlarsson

matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak