bug#44997: Flatpaks are invisible to application launchers

[John Kehayias]

I agree this should be exported by the flatpak package. I haven't hit any other 
packages putting anything in /etc/profile.d, though that does happen I know (so 
perhaps Guix should incorporate or patch such things?). Flatpak is also due for 
an update soon I think, so that would be a good time to make the modification 
perhaps.