packagekit: Merge systemd-updates plugin into the main plugin

There was no reason to keep it separate, and since commit 83f5653b, the systemd-updates plugin was no longer correctly matching with the packagekit plugin as the chosen management plugin of PackageKit apps and repos.

Rather than clearing the download size of apps to zero as part of a second pass in refine_async() (if they’re already prepared for an offline update), modify the code in packagekit-common.c which sets the download size in the first place, to correctly account for prepared updates.

This will probably fix offline update download size handling in other situations — this code is called by gs_plugin_url_to_app(). That code didn’t previously account for prepared offline updates.

Signed-off-by: Philip Withnall pwithnall@endlessos.org

Helps: #1472