pimd: Cleanup TODO file

pimd: Cleanup TODO file

The TODO file had become a dumping ground of changes made
to the protocol.  That when we modified the underlying code
we would need to update the TODO file again due to it's nature.

There is no point in keeping the list of items that we've done
as that commit messages will indicate the new features.  So
pull out all the Finished work and rework the Todo numbers
used.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>