[ML] Removing Custom Service Feature Flag (elastic#129780)

* Removing feature flag

* Removing missed references

(cherry picked from commit c7a5c59)

# Conflicts:
#	test/test-clusters/src/main/java/org/elasticsearch/test/cluster/FeatureFlag.java

Author: jonathan-buttner

test/test-clusters/src/main/java/org/elasticsearch/test/cluster/FeatureFlag.java

@@ -18,7 +18,6 @@
 public enum FeatureFlag {
     TIME_SERIES_MODE("es.index_mode_feature_flag_registered=true", Version.fromString("8.0.0"), null),
     SUB_OBJECTS_AUTO_ENABLED("es.sub_objects_auto_feature_flag_enabled=true", Version.fromString("8.16.0"), null),
-    INFERENCE_CUSTOM_SERVICE_ENABLED("es.inference_custom_service_feature_flag_enabled=true", Version.fromString("8.19.0"), null),
     LOGS_STREAM("es.logs_stream_feature_flag_enabled=true", Version.fromString("8.19.0"), null);
 
     public final String systemProperty;

x-pack/plugin/inference/qa/inference-service-tests/src/javaRestTest/java/org/elasticsearch/xpack/inference/BaseMockEISAuthServerTest.java

@@ -14,7 +14,6 @@
 import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.test.cluster.ElasticsearchCluster;
-import org.elasticsearch.test.cluster.FeatureFlag;
 import org.elasticsearch.test.cluster.local.distribution.DistributionType;
 import org.elasticsearch.test.rest.ESRestTestCase;
 import org.junit.ClassRule;
@@ -45,7 +44,6 @@ public class BaseMockEISAuthServerTest extends ESRestTestCase {
         // This plugin is located in the inference/qa/test-service-plugin package, look for TestInferenceServicePlugin
         .plugin("inference-service-test")
         .user("x_pack_rest_user", "x-pack-test-password")
-        .feature(FeatureFlag.INFERENCE_CUSTOM_SERVICE_ENABLED)
         .build();
 
     // The reason we're doing this is to make sure the mock server is initialized first so we can get the address before communicating

x-pack/plugin/inference/qa/inference-service-tests/src/javaRestTest/java/org/elasticsearch/xpack/inference/InferenceBaseRestTest.java

@@ -20,7 +20,6 @@
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.inference.TaskType;
 import org.elasticsearch.test.cluster.ElasticsearchCluster;
-import org.elasticsearch.test.cluster.FeatureFlag;
 import org.elasticsearch.test.cluster.local.distribution.DistributionType;
 import org.elasticsearch.test.rest.ESRestTestCase;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -51,7 +50,6 @@ public class InferenceBaseRestTest extends ESRestTestCase {
         .setting("xpack.security.enabled", "true")
         .plugin("inference-service-test")
         .user("x_pack_rest_user", "x-pack-test-password")
-        .feature(FeatureFlag.INFERENCE_CUSTOM_SERVICE_ENABLED)
         .build();
 
     @ClassRule

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/CustomServiceFeatureFlag.java

@@ -121,8 +121,6 @@
 import java.util.ArrayList;
 import java.util.List;
 
-import static org.elasticsearch.xpack.inference.CustomServiceFeatureFlag.CUSTOM_SERVICE_FEATURE_FLAG;
-
 public class InferenceNamedWriteablesProvider {
 
     private InferenceNamedWriteablesProvider() {}
@@ -186,10 +184,6 @@ public static List<NamedWriteableRegistry.Entry> getNamedWriteables() {
     }
 
     private static void addCustomNamedWriteables(List<NamedWriteableRegistry.Entry> namedWriteables) {
-        if (CUSTOM_SERVICE_FEATURE_FLAG.isEnabled() == false) {
-            return;
-        }
-
         namedWriteables.add(
             new NamedWriteableRegistry.Entry(ServiceSettings.class, CustomServiceSettings.NAME, CustomServiceSettings::new)
         );

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/InferenceNamedWriteablesProvider.java

@@ -151,10 +151,8 @@
 import java.util.Set;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
-import java.util.stream.Stream;
 
 import static java.util.Collections.singletonList;
-import static org.elasticsearch.xpack.inference.CustomServiceFeatureFlag.CUSTOM_SERVICE_FEATURE_FLAG;
 import static org.elasticsearch.xpack.inference.action.filter.ShardBulkInferenceActionFilter.INDICES_INFERENCE_BATCH_SIZE;
 import static org.elasticsearch.xpack.inference.common.InferenceAPIClusterAwareRateLimitingFeature.INFERENCE_API_CLUSTER_AWARE_RATE_LIMITING_FEATURE_FLAG;
 
@@ -384,11 +382,7 @@ public void loadExtensions(ExtensionLoader loader) {
     }
 
     public List<InferenceServiceExtension.Factory> getInferenceServiceFactories() {
-        List<InferenceServiceExtension.Factory> conditionalServices = CUSTOM_SERVICE_FEATURE_FLAG.isEnabled()
-            ? List.of(context -> new CustomService(httpFactory.get(), serviceComponents.get()))
-            : List.of();
-
-        List<InferenceServiceExtension.Factory> availableServices = List.of(
+        return List.of(
             context -> new HuggingFaceElserService(httpFactory.get(), serviceComponents.get()),
             context -> new HuggingFaceService(httpFactory.get(), serviceComponents.get()),
             context -> new OpenAiService(httpFactory.get(), serviceComponents.get()),
@@ -405,10 +399,9 @@ public List<InferenceServiceExtension.Factory> getInferenceServiceFactories() {
             context -> new JinaAIService(httpFactory.get(), serviceComponents.get()),
             context -> new VoyageAIService(httpFactory.get(), serviceComponents.get()),
             context -> new DeepSeekService(httpFactory.get(), serviceComponents.get()),
-            ElasticsearchInternalService::new
+            ElasticsearchInternalService::new,
+            context -> new CustomService(httpFactory.get(), serviceComponents.get())
         );
-
-        return Stream.concat(availableServices.stream(), conditionalServices.stream()).toList();
     }
 
     @Override