Update CPU manager feature enabling (#7390)

With `CPUManager` feature graduating to beta. No explicit enabling is
required starting v1.10.
References: kubernetes/kubernetes#55977

docs/tasks/administer-cluster/cpu-management-policies.md

@@ -33,9 +33,8 @@ management policies to determine some placement preferences on the node.
 
 ### Configuration
 
-The CPU Manager is introduced as an alpha feature in Kubernetes v1.8. It
-must be explicitly enabled in the kubelet feature gates:
-`--feature-gates=CPUManager=true`.
+The CPU Manager is an alpha feature in Kubernetes v1.8. It was enabled by
+default as a beta feature since v1.10.
 
 The CPU Manager policy is set with the `--cpu-manager-policy` kubelet
 option. There are two supported policies: