experimental-keystone-url and experimental-keystone-ca-file were always
experimental. So we don't need a deprecation period.
KeystoneAuthenticator was on the server side and needed userid/password
to be passed in and used that to authenticate with Keystone. We now
have authentication and authorization web hooks that can be used. There
is a external repo with a webook for keystone which works fine along
with the kubectl auth provider that was added in:
a0cebcb5

So we don't need this older style / hard coded / experimental code
anymore.