Remove `log4j_config` attribute

Was only needed for setting up ZooKeeper with a different configuration
file from what Kafka was using.
Remove `config` attribute

Was only needed for setting up ZooKeeper with a different configuration
file from what Kafka was using.
Use `jmx_port` directly from attribute

Previously ZooKeeper and Kafka had different JMX ports, but used the
same template for rendering the configuration file. Now that setting
up ZooKeeper is out of the picture we don’t need this anymore.