Remove content referring to keystone authentication (#8603)

Closes: #7411

content/cn/docs/admin/kube-apiserver.md

@@ -108,10 +108,6 @@ kube-apiserver
 
       --experimental-encryption-provider-config string          包含加密提供程序的配置的文件，该加密提供程序被用于在etcd中保存密钥。
 
-      --experimental-keystone-ca-file string                    如果设置该值，将会使用experimental-keystone-ca-file中的一个authority对Keystone服务的证书进行验证，否则将会使用主机的根CA进行验证。
-
-      --experimental-keystone-url string                        如果设置了该值，将启用keystone认证插件。
-
       --external-hostname string                                为此master生成外部URL时使用的主机名(例如Swagger API文档)。
 
       --feature-gates mapStringBool                             一个描述alpha/experimental特性开关的键值对列表。 选项包括:

content/en/docs/admin/authentication.md

@@ -536,29 +536,6 @@ checked.
 * `--requestheader-allowed-names` Optional.  List of common names (cn). If set, a valid client certificate with a Common Name (cn) in the specified list must be presented before the request headers are checked for user names. If empty, any Common Name is allowed.
 
 
-### Keystone Password
-
-Keystone authentication is enabled by passing the `--experimental-keystone-url=<AuthURL>`
-option to the API server during startup. The plugin is implemented in
-`plugin/pkg/auth/authenticator/password/keystone/keystone.go` and currently uses
-basic auth to verify user by username and password.
-
-If you have configured self-signed certificates for the Keystone server,
-you may need to set the `--experimental-keystone-ca-file=SOMEFILE` option when
-starting the Kubernetes API server. If you set the option, the Keystone
-server's certificate is verified by one of the authorities in the
-`experimental-keystone-ca-file`. Otherwise, the certificate is verified by
-the host's root Certificate Authority.
-
-For details on how to use keystone to manage projects and users, refer to the
-[Keystone documentation](http://docs.openstack.org/developer/keystone/). Please
-note that this plugin is still experimental, under active development, and likely
-to change in subsequent releases.
-
-Please refer to the [discussion](https://github.com/kubernetes/kubernetes/pull/11798#issuecomment-129655212),
-[blueprint](https://github.com/kubernetes/kubernetes/issues/11626) and [proposed
-changes](https://github.com/kubernetes/kubernetes/pull/25536) for more details.
-
 ## Anonymous requests
 
 When enabled, requests that are not rejected by other configured authentication methods are