keymutex: remove glog usage
keymutex: remove glog usage

https://github.com/kubernetes/utils/pull/55 was merged shortly after
https://github.com/kubernetes/utils/pull/68 and then brought back
glog, which now breaks vendoring of k8s.io/utils (can't have both glog
and klog defining the same command line flags).

Instead of replacing the logging with klog, logging gets removed
entirely. The rationale is that the log output is likely to be more
useful and/or readable if it is done by the caller. This is also a
first step towards removing the klog dependency from
k8s.io/utils (https://github.com/kubernetes/utils/pull/68#issuecomment-457249328).

kubernetes/utils,kubernetes/utils