chore!: remove setup-flatpaks

* it doesn't make sense with the module system anymore

usr/share/ublue-os/just/custom.just

@@ -1,13 +1,3 @@
 !include /usr/share/ublue-os/just/bling.just
 
-# Install all flatpaks defined in recipe.yml
-setup-flatpaks:
-  #!/usr/bin/env bash
-  echo 'Installing flatpaks from the ublue recipe ...'
-  flatpaks=$(yq -- '.firstboot.flatpaks[]' "/usr/share/ublue-os/recipe.yml")
-  for pkg in $flatpaks; do \
-      echo "Installing: ${pkg}" && \
-      flatpak install --user --noninteractive flathub $pkg; \
-  done
-
 # Include some of your custom scripts here!