Remove obsolete EMPTY_GROUPS constant in InvocableHandlerMethod

See gh-36274

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -81,8 +81,6 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private static final Mono<Object[]> EMPTY_ARGS = Mono.just(new Object[0]);
 
-	private static final Class<?>[] EMPTY_GROUPS = new Class<?>[0];
-
 	private static final Object NO_ARG_VALUE = new Object();
 
 	private static final boolean KOTLIN_REFLECT_PRESENT = KotlinDetector.isKotlinReflectPresent();