build: Remove flatpak dir from the dist'ed tarball

We don't need to the flatpak devel bits in the tarball, and neither
do we need the flathub shared-modules, including some Qt patches
with complicated licenses.
2 jobs for wip/hadess/remove-flatpak-dist-3-38 in 20 minutes and 1 second (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #1346450
build-fedora

00:06:26

passed #1346451
flatpak
flatpak:master

00:20:00