Description of problem:
Cloudn't disable machinehealthcheck by setting FeatureGates' spec value to {} according to the doc https://docs.openshift.com/container-platform/4.1/nodes/clusters/nodes-cluster-disabling-features.html

Version-Release number of selected component (if applicable):
$ oc get clusterversion
NAME      VERSION      AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.1.0-rc.3   True        False         44h     Cluster version is 4.1.0-rc.3

How reproducible:
Always

Steps to Reproduce:
1. Obtain the FeatureGate
$ oc get featuregate
NAME          AGE
cluster       45h
machine-api   18h

2. Edit FeatureGate machine-api setting the spec value to {}  to disable the Technology Preview features
3. Check machinehealthcheck feature removed or not

Actual results:
Couldn't disable machinehealthcheck by setting the FeatureGate's spec value to {}

$ oc get pod
NAME                                           READY   STATUS    RESTARTS   AGE
cluster-autoscaler-default-f8bf5fdc6-b9wvf     1/1     Running   0          18h
cluster-autoscaler-operator-7556b9fd94-cf5pc   1/1     Running   0          18h
machine-api-controllers-5c9fd97c6f-vdrx7       4/4     Running   0          18h
machine-api-operator-6755b6fb58-ks66t          1/1     Running   0          18h

$ oc logs -f machine-api-controllers-5c9fd97c6f-vdrx7 -c machine-healthcheck-controller
I0515 02:59:25.944646       1 machinehealthcheck_controller.go:112] Node ip-10-0-147-178.us-east-2.compute.internal is annotated with machine openshift-machine-api/zhsun4-cl6qv-worker-us-east-2b-rrckp
I0515 02:59:25.944727       1 machinehealthcheck_controller.go:169] Initialising remediation logic for machine zhsun4-cl6qv-worker-us-east-2b-rrckp
I0515 02:59:25.945042       1 machinehealthcheck_controller.go:273] ConfigMap node-unhealthy-conditions not found under the namespace openshift-machine-api, fallback to default values: items:
- name: Ready
  status: Unknown
  timeout: 300s
- name: Ready
  status: "False"
  timeout: 300s
I0515 02:59:25.945400       1 machinehealthcheck_controller.go:251] No remediaton action was taken. Machine zhsun4-cl6qv-worker-us-east-2b-rrckp with node ip-10-0-147-178.us-east-2.compute.internal is healthy

Expected results:
Could disable machinehealthcheck by setting the FeatureGate's spec value to {}

Additional info: