Remove support for RxJava 2.x as well

Includes realignment of Reactor adapter registration.

Closes gh-27443

src/docs/asciidoc/web-reactive.adoc

@@ -34,8 +34,6 @@ discussion of mock objects.
 response objects to provide support for testing WebFlux applications without an HTTP
 server. You can use the `WebTestClient` for end-to-end integration tests, too.
 
-
-
 include::rsocket.adoc[leveloffset=+1]
 
 
@@ -55,14 +53,8 @@ For annotated controllers, WebFlux transparently adapts to the reactive library
 the application. This is done with the help of the
 {api-spring-framework}/core/ReactiveAdapterRegistry.html[`ReactiveAdapterRegistry`], which
 provides pluggable support for reactive library and other asynchronous types. The registry
-has built-in support for RxJava 2/3, RxJava 1 (via RxJava Reactive Streams bridge), and
-`CompletableFuture`, but you can register others, too.
-
-[NOTE]
-====
-As of Spring Framework 5.3, support for RxJava 1 is deprecated.
-====
-
+has built-in support for RxJava 3, Kotlin coroutines and SmallRye Mutiny, but you can
+register others, too.
 
 For functional APIs (such as <<webflux-fn>>, the `WebClient`, and others), the general rules
 for WebFlux APIs apply -- `Flux` and `Mono` as return values and a Reactive Streams