Revert "Document new optional support for ConfigMap and Secret"

This reverts commit 7abcc6c854.

docs/user-guide/configmap/index.md

@@ -291,37 +291,6 @@ SPECIAL_LEVEL_KEY=very
 SPECIAL_TYPE_KEY=charm
 ```
 
-#### Optional ConfigMap in environment variables
-
-There might be situations where environment variables are not
-always required. These environment variables can be marked as optional in a
-pod like so:
-
-```yaml
-apiVersion: v1
-kind: Pod
-metadata:
-  name: dapi-test-pod
-spec:
-  containers:
-    - name: test-container
-      image: gcr.io/google_containers/busybox
-      command: [ "/bin/sh", "-c", "env" ]
-      env:
-        - name: SPECIAL_LEVEL_KEY
-          valueFrom:
-            configMapKeyRef:
-              name: a-config
-              key: akey
-              optional: true
-  restartPolicy: Never
-```
-
-When this pod is run, its output will include the lines:
-
-```shell
-```
-
 ### Use-Case: Set command-line arguments with ConfigMap
 
 ConfigMaps can also be used to set the value of the command or arguments in a container.  This is
@@ -453,38 +422,6 @@ very
 You can project keys to specific paths and specific permissions on a per-file
 basis. The [Secrets](/docs/user-guide/secrets/) user guide explains the syntax.
 
-#### Optional ConfigMap via volume plugin
-
-Volumes and files provided by a ConfigMap can be also be marked as optional.
-The ConfigMap or the key specified does not have to exist. The mount path for
-such items will always be created.
-
-```yaml
-apiVersion: v1
-kind: Pod
-metadata:
-  name: dapi-test-pod
-spec:
-  containers:
-    - name: test-container
-      image: gcr.io/google_containers/busybox
-      command: [ "/bin/sh", "-c", "ls /etc/config" ]
-      volumeMounts:
-      - name: config-volume
-        mountPath: /etc/config
-  volumes:
-    - name: config-volume
-      configMap:
-        name: no-config
-        optional: true
-  restartPolicy: Never
-```
-
-When this pod is run, the output will be:
-
-```shell
-```
-
 ## Real World Example: Configuring Redis
 
 Let's take a look at a real-world example: configuring redis using ConfigMap.  Say we want to inject
@@ -580,10 +517,9 @@ $ kubectl exec -it redis redis-cli
 
 ## Restrictions
 
-ConfigMaps must be created before they are consumed in pods unless they are
-marked as optional.  Controllers may be written to tolerate missing
-configuration data; consult individual components configured via ConfigMap on
-a case-by-case basis.
+ConfigMaps must be created before they are consumed in pods.  Controllers may be written to tolerate
+missing configuration data; consult individual components configured via ConfigMap on a case-by-case
+basis.
 
 ConfigMaps reside in a namespace.   They can only be referenced by pods in the same namespace.