Update WebFlux reference documentation

Note that WebFlux and WebFlux.fn can be both used at the same time
thanks to the handler mapping registration in `@EnableWebFlux`.

Fixing typos in the reference documentation for outdated Reactor
operators.

src/docs/asciidoc/web/web-flux-functional.adoc

@@ -108,7 +108,7 @@ a completion signal when the person has been read from the request and stored. S
 when the `Person` has been saved.
 <3> `getPerson` is a handler function that returns a single person, identified via the path
 variable `id`. We retrieve that `Person` via the repository, and create a JSON response if it is
-found. If it is not found, we use `otherwiseIfEmpty(Mono<T>)` to return a 404 Not Found response.
+found. If it is not found, we use `switchIfEmpty(Mono<T>)` to return a 404 Not Found response.
 
 ===== RouterFunctions
 

src/docs/asciidoc/web/web-flux.adoc

@@ -292,10 +292,6 @@ By default the starter runs with Reactor Netty but the dependencies can be chang
 with Spring Boot to switch to a different runtime.
 See the Spring Boot reference documentation page for more details and instruction.
 
-This starter also supports the functional web API and will detect automatically `RouterFunction`
-beans. Your Spring Boot WebFlux application should use the `RouterFunction` *or* the
-`RequestMapping` approach, it is not possible to mix them in the same application.
-
 [[web-reactive-getting-started-manual]]
 === Manual Bootstrapping