[Ros-release] Unstable.rosdistro cleanup

In preparation for Fuerte integration and bringup, the unstable.rosdistro
file is being cleaned up. We are removing entries that:

1. Are for unreleased stacks (version: null)
2. Are for stacks that have been broken for an extended period

This cleanup will enable bringup to go more quickly. If there are stacks
that you do not wish to be part of Fuerte, please help us by removing their
entries as well.

We'll send another update soon to give more status on the bringup of Fuerte.

cheers,
Ken