We had an extension for pulling out todo information from our docs. This
doesn't appear to have ever really been used though. Only a couple todo items
were published to the Cinder documentation, and the two published appear to
be extremely old.
Since this isn't really used and could just cause confusion, removing this
from the index page and removing the sphinx extension used to generate it.
Change-Id: I8993633538a5ee1687c4721bce3c520e8fb4ccfd
14f378a580