Simplify description for IdentifyPodOS

Now that the feature gate is removed, we can rely on the main Pod
documentation to explain what operating systems Kubernetes can support
for Pods.

Author: Tim Bannister

content/en/docs/reference/command-line-tools-reference/feature-gates/identify-pod-os.md

@@ -25,5 +25,3 @@ removed: true
 ---
 Allows the Pod OS field to be specified. This helps in identifying
 the OS of the pod authoritatively during the API server admission time.
-In Kubernetes {{< skew currentVersion >}}, the allowed values for the `pod.spec.os.name`
-are `windows` and `linux`.