trivial: Fix the build
trivial: Fix the build

Keep on using _cleanup_object_unref_ for SoupSession until
https://bugzilla.gnome.org/show_bug.cgi?id=754721 is upstreamed.

superm1/appstream-glib,mitya57/appstream-glib,superm1/appstream-glib,hughsie/appstream-glib,hughsie/appstream-glib,ikeydoherty/appstream-glib,ximion/appstream-glib,ximion/appstream-glib,ximion/appstream-glib,mitya57/appstream-glib,hughsie/appstream-glib,ikeydoherty/appstream-glib