KAFKA-19900: Fix the documentation for remove controller (#20931)

This PR removes the mention to KIP-996 when it comes to remove a
controller because such KIP is now implemented and already included into
Apache Kafka (since 4.0.0) so the correct sequence is always remove the
controller first and the shut down it.

Reviewers: Mickael Maison <mickael.maison@gmail.com>, Luke Chen <showuon@gmail.com>

Signed-off-by: Paolo Patierno <ppatierno@live.com>

Author: ppatierno

docs/ops.html

@@ -4161,7 +4161,7 @@ <h5 class="anchor-heading"><a id="kraft_reconfig_add" class="anchor-link"></a><a
     please also include in the "controller.properties".</p>
 
   <h5 class="anchor-heading"><a id="kraft_reconfig_remove" class="anchor-link"></a><a href="#kraft_reconfig_remove">Remove Controller</a></h5>
-  If the dynamic controller cluster already exists, it can be shrunk using the <code>bin/kafka-metadata-quorum.sh remove-controller</code> command. Until KIP-996: Pre-vote has been implemented and released, it is recommended to shutdown the controller that will be removed before running the remove-controller command.
+  If the dynamic controller cluster already exists, it can be shrunk using the <code>bin/kafka-metadata-quorum.sh remove-controller</code> command. Use the remove-controller command before shutting down the controller to have it removed from the quorum first.
 
   When using broker endpoints use the --bootstrap-server flag:
   <pre><code class="language-bash">$ bin/kafka-metadata-quorum.sh --bootstrap-server localhost:9092 remove-controller --controller-id &lt;id&gt; --controller-directory-id &lt;directory-id&gt;</code></pre>