Restore ZKUtil.deleteRecursive in order to help compatibility of applications with 3.5 and 3.6

In HerdDB project (https://github.com/diennea/herddb) we are using BookKeeper that in turn uses ZKUtil.deleteRecursive and we are not able to switch to ZooKeeper 3.6.0

This is the error:
java.lang.NoSuchMethodError: org.apache.zookeeper.ZKUtil.deleteRecursive(Lorg/apache/zookeeper/ZooKeeper;Ljava/lang/String;)V
Apart a fix BookKeeper (https://github.com/apache/bookkeeper/issues/2292), we should take into consideration to restore that signature (adding some dummy method that calls the new one) in order to ease adoption of ZooKeeper 3.6.x

In fact it is very common that an application uses multiple ZooKeeper based libraries, like HBase, BookKeeper, Pulsar, Kafka...and the user cannot upgrade to 3.6 until every other dependency is able to work with 3.6.0.

If the fix is easy, like in this case, it is worth to help the community