Automatic merge from submit-queue
kubelet: Remove redundant `Container.Created`
As far as I can tell, this has been supplanted by a) the `DockerJSON.CreatedAt` field and b) the
`ContainerStatus.CreatedAt`, where the first is used for creating the
second.
The `.Created` field was only written to as far as I can see.
cc @yifan-gu & @Random-Liu
Is there any reason we might want to keep this around?