Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
dockershim: remove the use of kubelet's internal API
We let dockershim implement the kubelet's internal (CRI) API as an
intermediary step before transitioning fully to communicate using gRPC.
Now that kubelet has been communicating to the runtime over gRPC for
multiple releases, we can safely retire the extra interface in
dockershim.
This PR also moves the legacy functions to a separate file and clean up
the interfaces.
bfac95e71b