Automatic merge from submit-queue (batch tested with PRs 42835, 42974)

remove legacy insecure port options from genericapiserver

The insecure port has been a source of problems and it will prevent proper aggregation into a cluster, so the genericapiserver has no need for it.  In addition, there's no reason for it to be in the main kube-apiserver flow either.  This pull removes it from genericapiserver and removes it from the shared kube-apiserver code.  It's still wired up in the command, but its no longer possible for someone to mess up and start using in mainline code.

@kubernetes/sig-api-machinery-misc @ncdc