build-aux: switch flatpak manifest to librest-1.0

librest-0.7 uses libsoup 2 and fails to build since it was removed from the runtime. Even if it did build successfully, gnome-control-center would crash at runtime because it links to libsoup 3 dependencies like gnome-online-accounts. The solution is simple: use librest-1.0 instead.

Note that nobody is using this flatpak manifest. gnome-online-accounts switched to libsoup 3 last release cycle. There is no way for this manifest to have worked since that time because it builds the master branch of gnome-online-accounts.

Fixes #2324 (closed)