Remove consistency check from /binding.

I'm proposing to remove the consistency check from the master and to add it to the kubelet in a future PR.  I'll file an issue for that second step if this is merged.

Here are several reasons why I think the consistency check is better done in the kubelet:
 1. I want to have kubelets watch /pods (not /boundPods) and the consistency check can't be done for pods.
 1. The atomicity provided by doing this check in the master is an illusion: kubelets do setup and teardown of pods asynchronously, afaics.  A conflict can exist during this overlap period, which experience has shown can be longer that one might expect.  If you want to really ensure no conflicts you need to order deletes and creates in kubelet.  
 1. The kubelet may have information about conflicts which are not available to the master, such as local file config.