Fix bad source version in ServiceProcessor (#410)

Author: slinkydeveloper

sdk-api-gen/src/main/java/dev/restate/sdk/gen/ServiceProcessor.java

@@ -28,7 +28,7 @@
 import javax.tools.StandardLocation;
 
 @SupportedAnnotationTypes("*")
-@SupportedSourceVersion(SourceVersion.RELEASE_11)
+@SupportedSourceVersion(SourceVersion.RELEASE_17)
 public class ServiceProcessor extends AbstractProcessor {
 
   private HandlebarsTemplateEngine definitionsCodegen;
@@ -38,11 +38,6 @@ public class ServiceProcessor extends AbstractProcessor {
   private static final Set<String> RESERVED_METHOD_NAMES =
       Set.of("send", "submit", "workflowHandle");
 
-  @Override
-  public SourceVersion getSupportedSourceVersion() {
-    return SourceVersion.RELEASE_17;
-  }
-
   @Override
   public synchronized void init(ProcessingEnvironment processingEnv) {
     super.init(processingEnv);