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 in 19 minutes and 43 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #1346448
build-fedora

00:05:20

passed #1346449
flatpak
flatpak:master

00:19:42