Remove all manual accounting of connected user bundles
IO used to manually keep a list of user bundles it was connected to, but
it didn't work correctly: sometimes it didn't notice that a bundle
wasn't connected anymore, and the list wasn't correctly persisted across
save/reloads among other things.
Moreover, it wasn't needed at all, since the user bundles are correctly
listed by _session.bundles() and IO already notices they are connected !
Remove all occurrences of |_bundles_connected| and |check_bundles_connected|.