[SPARK-38968][K8S] Remove a variable hadoopConf from KerberosConfDriverFeatureStep

### What changes were proposed in this pull request?

This PR removes a variable `hadoopConf` from `KerberosConfDriverFeatureStep`.

### Why are the changes needed?

#22959 added a variable `hadoopConf` to generate `tokenManager`. And, #22911 removed `tokenManager` and `buildKerberosSpec`, so `hadoopConf` is no-use.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Pass the GA.

Closes #36283 from dcoliversun/SPARK-38968.

Authored-by: Qian.Sun <[email protected]>
Signed-off-by: Sean Owen <[email protected]>

Author: dcoliversun

resource-managers/kubernetes/core/src/main/scala/org/apache/spark/deploy/k8s/features/KerberosConfDriverFeatureStep.scala

@@ -57,7 +57,6 @@ private[spark] class KerberosConfDriverFeatureStep(kubernetesConf: KubernetesDri
   private val existingSecretItemKey = kubernetesConf.get(KUBERNETES_KERBEROS_DT_SECRET_ITEM_KEY)
   private val krb5File = kubernetesConf.get(KUBERNETES_KERBEROS_KRB5_FILE)
   private val krb5CMap = kubernetesConf.get(KUBERNETES_KERBEROS_KRB5_CONFIG_MAP)
-  private val hadoopConf = SparkHadoopUtil.get.newConfiguration(kubernetesConf.sparkConf)
 
   KubernetesUtils.requireNandDefined(
     krb5File,