Stop referring to "JDK 8" features in documentation

See gh-36310

framework-docs/modules/ROOT/pages/integration/scheduling.adoc

@@ -533,8 +533,7 @@ that returns a value:
 ----
 
 TIP: `@Async` methods may not only declare a regular `java.util.concurrent.Future` return
-type but also Spring's `org.springframework.util.concurrent.ListenableFuture` or, as of
-Spring 4.2, JDK 8's `java.util.concurrent.CompletableFuture`, for richer interaction with
+type but also `java.util.concurrent.CompletableFuture`, for richer interaction with
 the asynchronous task and for immediate composition with further processing steps.
 
 You can not use `@Async` in conjunction with lifecycle callbacks such as `@PostConstruct`.

framework-docs/modules/ROOT/pages/web/webflux-functional.adoc

@@ -13,9 +13,9 @@ the same xref:web/webflux/reactive-spring.adoc[Reactive Core] foundation.
 == Overview
 [.small]#xref:web/webmvc-functional.adoc#webmvc-fn-overview[See equivalent in the Servlet stack]#
 
-In WebFlux.fn, an HTTP request is handled with a `HandlerFunction`: a function that takes
+In WebFlux.fn, an HTTP request is handled with a `HandlerFunction`: a function that takes a
 `ServerRequest` and returns a delayed `ServerResponse` (i.e. `Mono<ServerResponse>`).
-Both the request and the response object have immutable contracts that offer JDK 8-friendly
+Both the request and the response object have immutable contracts that offer convenient
 access to the HTTP request and response.
 `HandlerFunction` is the equivalent of the body of a `@RequestMapping` method in the
 annotation-based programming model.
@@ -117,7 +117,7 @@ Most applications can run through the WebFlux Java configuration, see xref:web/w
 == HandlerFunction
 [.small]#xref:web/webmvc-functional.adoc#webmvc-fn-handler-functions[See equivalent in the Servlet stack]#
 
-`ServerRequest` and `ServerResponse` are immutable interfaces that offer JDK 8-friendly
+`ServerRequest` and `ServerResponse` are immutable interfaces that offer convenient
 access to the HTTP request and response.
 Both request and response provide {reactive-streams-site}[Reactive Streams] back pressure
 against the body streams.

framework-docs/modules/ROOT/pages/web/webmvc-functional.adoc

@@ -15,7 +15,7 @@ the same xref:web/webmvc/mvc-servlet.adoc[DispatcherServlet].
 
 In WebMvc.fn, an HTTP request is handled with a `HandlerFunction`: a function that takes
 `ServerRequest` and returns a `ServerResponse`.
-Both the request and the response object have immutable contracts that offer JDK 8-friendly
+Both the request and the response object have immutable contracts that offer convenient
 access to the HTTP request and response.
 `HandlerFunction` is the equivalent of the body of a `@RequestMapping` method in the
 annotation-based programming model.
@@ -116,7 +116,7 @@ xref:web/webmvc-functional.adoc#webmvc-fn-running[Running a Server].
 == HandlerFunction
 [.small]#xref:web/webflux-functional.adoc#webflux-fn-handler-functions[See equivalent in the Reactive stack]#
 
-`ServerRequest` and `ServerResponse` are immutable interfaces that offer JDK 8-friendly
+`ServerRequest` and `ServerResponse` are immutable interfaces that offer convenient
 access to the HTTP request and response, including headers, body, method, and status code.
 
 [[webmvc-fn-request]]

framework-docs/modules/ROOT/pages/web/webmvc/mvc-controller/ann-methods/arguments.adoc

@@ -6,7 +6,7 @@
 The next table describes the supported controller method arguments. Reactive types are not supported
 for any arguments.
 
-JDK 8's `java.util.Optional` is supported as a method argument in combination with
+`java.util.Optional` is supported as a method argument in combination with
 annotations that have a `required` attribute (for example, `@RequestParam`, `@RequestHeader`,
 and others) and is equivalent to `required=false`.