all: deprecate v1 support

Etcd moves to 0.5 without the support of v1.

@xiangli-cmu @philips
The resource is not really there anymore though, it's gone. The URL does not returns the expected resources anymore.

`403 Forbidden` is reserved for clients without the necessary clearance to see the resource, not for when a resource is removed. On the other hand, `410 Gone` exists exactly to represent this case.