MINOR: Remove ZooKeeper mentions in Admin javadoc (apache#18531)

Reviewers: Chia-Ping Tsai <[email protected]>

Author: mimaison

clients/src/main/java/org/apache/kafka/clients/admin/Admin.java

@@ -1520,8 +1520,7 @@ default DescribeMetadataQuorumResult describeMetadataQuorum() {
     /**
      * Unregister a broker.
      * <p>
-     * This operation does not have any effect on partition assignments. It is supported
-     * only on Kafka clusters which use Raft to store metadata, rather than ZooKeeper.
+     * This operation does not have any effect on partition assignments.
      *
      * This is a convenience method for {@link #unregisterBroker(int, UnregisterBrokerOptions)}
      *
@@ -1537,17 +1536,15 @@ default UnregisterBrokerResult unregisterBroker(int brokerId) {
     /**
      * Unregister a broker.
      * <p>
-     * This operation does not have any effect on partition assignments. It is supported
-     * only on Kafka clusters which use Raft to store metadata, rather than ZooKeeper.
+     * This operation does not have any effect on partition assignments.
      *
      * The following exceptions can be anticipated when calling {@code get()} on the future from the
      * returned {@link UnregisterBrokerResult}:
      * <ul>
      *   <li>{@link org.apache.kafka.common.errors.TimeoutException}
      *   If the request timed out before the describe operation could finish.</li>
      *   <li>{@link org.apache.kafka.common.errors.UnsupportedVersionException}
-     *   If the software is too old to support the unregistration API, or if the
-     *   cluster is not using Raft to store metadata.
+     *   If the software is too old to support the unregistration API.
      * </ul>
      * <p>
      *