builder: Drop the storing of local files to data: uris
builder: Drop the storing of local files to data: uris

This just risks making the manifest very large, in case some
file is large, and it didn't even solve the whole problem,
which bundling sources is.

matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,GeorgesStavracas/flatpak,matthiasclasen/flatpak,flatpak/flatpak,GeorgesStavracas/flatpak,flatpak/flatpak,GeorgesStavracas/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,GeorgesStavracas/flatpak,flatpak/flatpak,matthiasclasen/flatpak,GeorgesStavracas/flatpak