Unfortunately, there's not much to be done from the outside. A lawsuit is pending, according to the article, and I strongly suspect that the city will lose. My understanding is that service animals are generally exempted from laws like this. (As an aside, I don't agree with breed laws anyway, since it's more the training and treatment of the animal in question that creates a dangerous critter.)
JKS, you are correct. Service animals are exempt from breed bans. It amounts to discrimination under the Americans with Disabilities Act, and the city council can't ban his dog any more than they could legally ban Jews or Asians.
Any intelligent jury would take the city to the cleaners. The problem is that juries are not necessarily intelligent. I hope he wins, as it would strike a blow for the entire service animal community.