o Code simplification and refactoring:

    - Remove our old, non-weighted bandwidth-based node selection code.
      Previously, we used it as a fallback when we couldn't perform
      weighted bandwidth-based node selection.  But that would only
      happen in the cases where we had no consensus, or when we had a
      consensus generated by buggy or ancient directory authorities.  In
      either case, it's better to use the more modern, better maintained
      algorithm, with reasonable defaults for the weights. Closes
      ticket 13126.