Remove initializers feature gate (#14602)

* Remove initializers feature gate

Initializers are removed in 1.14
kubernetes/kubernetes#72972

* Update feature-gates.md

content/en/docs/reference/setup-tools/kubeadm/implementation-details.md

@@ -108,7 +108,7 @@ In any case the user can skip specific preflight checks (or eventually all prefl
 - [warning] if extra arg flags for API server, controller manager,  scheduler contains some invalid options
 - [warning] if connection to https://API.AdvertiseAddress:API.BindPort goes through proxy
 - [warning] if connection to services subnet goes through proxy (only first address checked)
-- [warning] if connection to Pods subnet goes through proxy (only first address checked)  
+- [warning] if connection to Pods subnet goes through proxy (only first address checked)
 - If external etcd is provided:
   - [Error] if etcd version less than 3.0.14
   - [Error] if etcd certificates or keys are specified, but not provided
@@ -235,7 +235,6 @@ Other API server flags that are set unconditionally are:
  - `--allow-privileged` to `true` (required e.g. by kube proxy)
  - `--requestheader-client-ca-file` to `front-proxy-ca.crt`
  - `--enable-admission-plugins` to:
-    - [`Initializers`](/docs/reference/access-authn-authz/admission-controllers/#initializers-alpha) to enable [Dynamic Admission Control](/docs/reference/access-authn-authz/extensible-admission-controllers/).
     - [`NamespaceLifecycle`](/docs/reference/access-authn-authz/admission-controllers/#namespacelifecycle) e.g. to avoid deletion of
       system reserved namespaces
     - [`LimitRanger`](/docs/reference/access-authn-authz/admission-controllers/#limitranger) and [`ResourceQuota`](/docs/reference/access-authn-authz/admission-controllers/#resourcequota) to enforce limits on namespaces
@@ -379,7 +378,7 @@ existing cluster; for more details see also [design proposal](https://github.com
 setting API server and controller flags as already described in previous paragraphs.
 Please note that:
 
-1. TLS bootstrapping for nodes can be configured with the [`kubeadm init phase bootstrap-token`](/docs/reference/setup-tools/kubeadm/kubeadm-init-phase/#cmd-phase-bootstrap-token)  
+1. TLS bootstrapping for nodes can be configured with the [`kubeadm init phase bootstrap-token`](/docs/reference/setup-tools/kubeadm/kubeadm-init-phase/#cmd-phase-bootstrap-token)
    command, executing all the configuration steps described in following paragraphs; alternatively, each step can be invoked individually
 
 #### Create a bootstrap token