Fix compilation for custom authz engine example (elastic#125547)

Relates: elastic#125469

Author: ywangd

plugins/examples/security-authorization-engine/src/main/java/org/elasticsearch/example/CustomAuthorizationEngine.java

@@ -18,8 +18,6 @@
 import org.elasticsearch.xpack.core.security.authc.Authentication;
 import org.elasticsearch.xpack.core.security.authc.Subject;
 import org.elasticsearch.xpack.core.security.authz.AuthorizationEngine;
-import org.elasticsearch.xpack.core.security.authz.AuthorizationEngine.PrivilegesToCheck;
-import org.elasticsearch.xpack.core.security.authz.AuthorizationEngine.PrivilegesCheckResult;
 import org.elasticsearch.xpack.core.security.authz.ResolvedIndices;
 import org.elasticsearch.xpack.core.security.authz.RoleDescriptor;
 import org.elasticsearch.xpack.core.security.authz.RoleDescriptor.IndicesPrivileges;
@@ -118,7 +116,7 @@ public void loadAuthorizedIndices(
         if (isSuperuser(requestInfo.getAuthentication().getEffectiveSubject().getUser())) {
             listener.onResponse(new AuthorizedIndices() {
                 public Set<String> all(IndexComponentSelector selector) {
-                    return () -> indicesLookup.keySet();
+                    return indicesLookup.keySet();
                 }
                 public boolean check(String name, IndexComponentSelector selector) {
                     return indicesLookup.containsKey(name);
@@ -127,7 +125,7 @@ public boolean check(String name, IndexComponentSelector selector) {
         } else {
             listener.onResponse(new AuthorizedIndices() {
                 public Set<String> all(IndexComponentSelector selector) {
-                    return () -> Set.of();
+                    return Set.of();
                 }
                 public boolean check(String name, IndexComponentSelector selector) {
                     return false;

plugins/examples/security-authorization-engine/src/test/java/org/elasticsearch/example/CustomAuthorizationEngineTests.java

@@ -11,8 +11,6 @@
 
 import org.elasticsearch.action.search.SearchRequest;
 import org.elasticsearch.action.support.PlainActionFuture;
-import org.elasticsearch.cluster.metadata.IndexAbstraction;
-import org.elasticsearch.cluster.metadata.IndexAbstraction.ConcreteIndex;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.common.settings.Settings;
@@ -30,9 +28,6 @@
 import org.elasticsearch.xpack.core.security.user.User;
 
 import java.util.Collections;
-import java.util.HashMap;
-import java.util.Map;
-import java.util.stream.Stream;
 
 import static org.hamcrest.Matchers.is;