Refguide: Remove mention of discouraged subscribe variant

This commit removes the mention of the subscribe variant that takes a
Consumer<Subscription> from the reference guide.
This method is deprecated in order to discourage it, as it is easy to
misuse it and cause hanging when no request is explicitly made by
the Consumer.

Fixes #3090.

docs/asciidoc/subscribe-details.adoc

@@ -106,26 +106,6 @@ Done
 ----
 ====
 
-The last signature of the `subscribe` method includes a `Consumer<Subscription>`.
-
-NOTE: That variant requires you to do something with the `Subscription` (perform a
-`request(long)` on it or `cancel()` it). Otherwise the `Flux` hangs.
-
-The following example shows the last signature of the `subscribe` method:
-
-====
-[source,java]
-----
-Flux<Integer> ints = Flux.range(1, 4);
-ints.subscribe(i -> System.out.println(i),
-    error -> System.err.println("Error " + error),
-    () -> System.out.println("Done"),
-    sub -> sub.request(10)); <1>
-----
-<1> When we subscribe we receive a `Subscription`. Signal that we want up to `10`
-elements from the source (which will actually emit 4 elements and complete).
-====
-
 === Cancelling a `subscribe()` with Its `Disposable`
 
 All these lambda-based variants of `subscribe()` have a `Disposable` return type.