Flatpak has API called flatpak_installation_list_remotes_by_type() which
can list dynamic (LAN/USB) remotes that mirror configured remotes in an
installation. It does this by searching them for the appstream/<arch>
ref, such as appstream/x86_64. But Flatpak now supports
appstream2/<arch> as a way to provide the appstream data as uncompressed
XML, and it's possible that a USB created with `flatpak create-usb` (or
a LAN peer) only has the appstream2 ref available for a certain
collection ID. So this commit changes
list_remotes_for_configured_remote() so that it looks for both
appstream/<arch> and appstream2/<arch>, which makes
flatpak_installation_list_remotes_by_type() robust to that scenario.
e9d9f54ab8