Proper WebFlux reference and MVC reference updates

Pending -- WebSocket, WebTestClient, more details around annotation
processing, exception handling, and view resolution.

Issue: SPR-15149, SPR-16009

src/docs/asciidoc/integration.adoc

@@ -1369,68 +1369,8 @@ and writes the media type supported by the Java I/O API.
 [[rest-async-resttemplate]]
 ==== Async RestTemplate
 
-Web applications often need to query external REST services those days. The very nature of
-HTTP and synchronous calls can lead up to challenges when scaling applications for those
-needs: multiple threads may be blocked, waiting for remote HTTP responses.
-
-`AsyncRestTemplate` and <<rest-resttemplate>>'s APIs are very similar; see
-<<rest-overview-of-resttemplate-methods-tbl>>. The main difference between those APIs is
-that `AsyncRestTemplate` returns
-{api-spring-framework}/util/concurrent/ListenableFuture.html[`ListenableFuture`]
-wrappers as opposed to concrete results.
-
-The previous `RestTemplate` example translates to:
-
-[source,java,indent=0]
-[subs="verbatim,quotes"]
-----
-	// async call
-	Future<ResponseEntity<String>> futureEntity = template.getForEntity(
-		"http://example.com/hotels/{hotel}/bookings/{booking}", String.class, "42", "21");
-
-	// get the concrete result - synchronous call
-	ResponseEntity<String> entity = futureEntity.get();
-----
-
-{api-spring-framework}/util/concurrent/ListenableFuture.html[`ListenableFuture`]
-accepts completion callbacks:
-
-[source,java,indent=0]
-[subs="verbatim,quotes"]
-----
-	ListenableFuture<ResponseEntity<String>> futureEntity = template.getForEntity(
-		"http://example.com/hotels/{hotel}/bookings/{booking}", String.class, "42", "21");
-
-	// register a callback
-	futureEntity.addCallback(new ListenableFutureCallback<ResponseEntity<String>>() {
-		@Override
-		public void onSuccess(ResponseEntity<String> entity) {
-			//...
-		}
-
-		@Override
-		public void onFailure(Throwable t) {
-			//...
-		}
-	});
-----
-
-[NOTE]
-====
-The default `AsyncRestTemplate` constructor registers a
-{api-spring-framework}/core/task/SimpleAsyncTaskExecutor.html[`SimpleAsyncTaskExecutor`
-] for executing HTTP requests.
-When dealing with a large number of short-lived requests, a thread-pooling TaskExecutor
-implementation like
-{api-spring-framework}/scheduling/concurrent/ThreadPoolTaskExecutor.html[`ThreadPoolTaskExecutor`]
-may be a good choice.
-====
-
-See the
-{api-spring-framework}/util/concurrent/ListenableFuture.html[`ListenableFuture` javadocs]
-and
-{api-spring-framework}/web/client/AsyncRestTemplate.html[`AsyncRestTemplate` javadocs]
-for more details.
+The `AsyncRestTemplate` is deprecated.
+Please use the <<web-reactive.adoc#webflux-client,WebClient>> instead.