Cleaning up SIG maintainers

[Jonathan Berkhahn]

I'm preparing to move our repos over to the Kubernetes-Sigs org on Github. As part of this process I'm going to be removing a lot of maintainers that are no longer active and aren't members of the Kubernetes-Sigs.

If you'd like to retain your maintainer status or believe you've been removed in error, please message me.

Thanks,

-Jonathan