remove redundant error checks in mark/unmark deletion functions

This change removes a few nil checks against resources returned in the
Mark and Unmark deletion functions of the cluster-autoscaler CAPI
provider. These checks look to see if the returned value for a resource
are nil, but the function will not return nil if it returns an
error[0]. We only need to check the error return as discussed here[1].

[0]
https://github.com/kubernetes/client-go/blob/master/dynamic/simple.go#L234
[1]
https://github.com/openshift/kubernetes-autoscaler/pull/141/files#r414480960

cluster-autoscaler/cloudprovider/clusterapi/clusterapi_machinedeployment.go

@@ -138,13 +138,9 @@ func (r machineDeploymentScalableResource) UnmarkMachineForDeletion(machine *Mac
 
 func (r machineDeploymentScalableResource) MarkMachineForDeletion(machine *Machine) error {
 	u, err := r.controller.dynamicclient.Resource(*r.controller.machineResource).Namespace(machine.Namespace).Get(context.TODO(), machine.Name, metav1.GetOptions{})
-
 	if err != nil {
 		return err
 	}
-	if u == nil {
-		return fmt.Errorf("unknown machine %s", machine.Name)
-	}
 
 	u = u.DeepCopy()
 

cluster-autoscaler/cloudprovider/clusterapi/clusterapi_machineset.go

@@ -102,13 +102,9 @@ func (r machineSetScalableResource) SetSize(nreplicas int32) error {
 
 func (r machineSetScalableResource) MarkMachineForDeletion(machine *Machine) error {
 	u, err := r.controller.dynamicclient.Resource(*r.controller.machineResource).Namespace(machine.Namespace).Get(context.TODO(), machine.Name, metav1.GetOptions{})
-
 	if err != nil {
 		return err
 	}
-	if u == nil {
-		return fmt.Errorf("unknown machine %s", machine.Name)
-	}
 
 	u = u.DeepCopy()
 

cluster-autoscaler/cloudprovider/clusterapi/clusterapi_scalableresource.go

@@ -16,6 +16,12 @@ limitations under the License.
 
 package clusterapi
 
+import (
+	"context"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
 // scalableResource is a resource that can be scaled up and down by
 // adjusting its replica count field.
 type scalableResource interface {
@@ -50,3 +56,19 @@ type scalableResource interface {
 	// UnmarkMachineForDeletion unmarks machine for deletion
 	UnmarkMachineForDeletion(machine *Machine) error
 }
+
+func unmarkMachineForDeletion(controller *machineController, machine *Machine) error {
+	u, err := controller.dynamicclient.Resource(*controller.machineResource).Namespace(machine.Namespace).Get(context.TODO(), machine.Name, metav1.GetOptions{})
+	if err != nil {
+		return err
+	}
+
+	annotations := u.GetAnnotations()
+	if _, ok := annotations[machineDeleteAnnotationKey]; ok {
+		delete(annotations, machineDeleteAnnotationKey)
+		u.SetAnnotations(annotations)
+		_, updateErr := controller.dynamicclient.Resource(*controller.machineResource).Namespace(u.GetNamespace()).Update(context.TODO(), u, metav1.UpdateOptions{})
+		return updateErr
+	}
+	return nil
+}