RBAC Migration Followup #5: Delete policy registry code and associated commands

[enj]

• Delete all legacy policy registry code and related commands like overwrite bootstrap policy
• Find callers of clusterpolicyregistry "github.com/openshift/origin/pkg/authorization/registry/clusterpolicy" and move to point of use, fixed in move old direct etcd methods for policy closer to source #15863

[enj]

@openshift/cli-review putting this a proposed 3.8 issue to delete all of this stuff.