extra-data: Simplify extra-data progress setup
extra-data: Simplify extra-data progress setup

We need to get the commit object to setup the extra-data progress information,
and this is currently done using a complex pull operation to a temporary
repo. According to https://github.com/flatpak/flatpak/issues/3515 it
even causes an unecessary download of the summary in some cases.

Now that we don't need to support p2p we can instead directly download
the commit object using a simple http operation (or from the sideload
repos), as we know the commit id at this point anyway.

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak