[ML] Minor tidyups in ML serverless extension (#101039)

Followup to #99129 and #100956

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/DefaultMachineLearningExtension.java

@@ -56,6 +56,7 @@ public class DefaultMachineLearningExtension implements MachineLearningExtension
         return ANALYTICS_DEST_INDEX_ALLOWED_SETTINGS;
     }
 
+    @Override
     public AbstractNodeAvailabilityZoneMapper getNodeAvailabilityZoneMapper(Settings settings, ClusterSettings clusterSettings) {
         return new NodeRealAvailabilityZoneMapper(settings, clusterSettings);
     }

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MachineLearningExtension.java

@@ -10,7 +10,6 @@ package org.elasticsearch.xpack.ml;
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.xpack.ml.autoscaling.AbstractNodeAvailabilityZoneMapper;
-import org.elasticsearch.xpack.ml.autoscaling.NodeRealAvailabilityZoneMapper;
 
 public interface MachineLearningExtension {
 
@@ -26,11 +25,7 @@ public interface MachineLearningExtension {
 
     boolean isNlpEnabled();
 
-    default String[] getAnalyticsDestIndexAllowedSettings() {
-        return DefaultMachineLearningExtension.ANALYTICS_DEST_INDEX_ALLOWED_SETTINGS;
-    }
+    String[] getAnalyticsDestIndexAllowedSettings();
 
-    default AbstractNodeAvailabilityZoneMapper getNodeAvailabilityZoneMapper(Settings settings, ClusterSettings clusterSettings) {
-        return new NodeRealAvailabilityZoneMapper(settings, clusterSettings);
-    }
+    AbstractNodeAvailabilityZoneMapper getNodeAvailabilityZoneMapper(Settings settings, ClusterSettings clusterSettings);
 }