manifest: Drop fallback mode components
manifest: Drop fallback mode components

See http://git.gnome.org/browse/jhbuild/commit/?id=ef31a2cd06e3846b7f81a20c27d16916d9e4b9fa

djdeath/gnome-ostree,djdeath/gnome-ostree,GNOME/gnome-ostree,chergert/gnome-continuous,vrutkovs/vrutkovs.github.io,GNOME/gnome-ostree,vrutkovs/vrutkovs.github.io,chergert/gnome-continuous,djdeath/gnome-ostree,GNOME/gnome-ostree,vrutkovs/vrutkovs.github.io,chergert/gnome-continuous