Polish timed operators and remove useTimer()

spring-web-reactive/src/test/java/org/springframework/http/server/reactive/AsyncIntegrationTests.java

@@ -65,7 +65,6 @@ public class AsyncIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 		@Override
 		public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
 			return response.writeWith(Flux.just("h", "e", "l", "l", "o")
-			                            .useTimer(Schedulers.timer())
 			                            .delay(Duration.ofMillis(100))
 			                            .publishOn(asyncGroup)
 					.collect(dataBufferFactory::allocateBuffer, (buffer, str) -> buffer.write(str.getBytes())));