Remove invalid example of spring.mvc.async.request-timout property

See gh-19057

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcProperties.java

@@ -207,8 +207,7 @@ public class WebMvcProperties {
 
 		/**
 		 * Amount of time before asynchronous request handling times out. If this value is
-		 * not set, the default timeout of the underlying implementation is used, e.g. 10
+		 * not set, the default timeout of the underlying implementation is used.
-		 * seconds on Tomcat with Servlet 3.
 		 */
 		private Duration requestTimeout;