MINOR: Remove zk from replica_verification_test

[frankvicky]

We could remove zk from the replica_verification_test since ak has eliminated zk.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[m1a2st]

Thanks for this PR, left a comment

[m1a2st]

Could you also rename num_zk this field?

[frankvicky]

https://issues.apache.org/jira/browse/KAFKA-18582
This is tracking by this issue.

[chia7712]

I don't dig in it, but this PR seems to cause another failure

    TimeoutError("Kafka server didn't finish startup in 60 seconds")
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/ducktape/tests/runner_client.py", line 351, in _do_run
    data = self.run_test()
  File "/usr/local/lib/python3.7/dist-packages/ducktape/tests/runner_client.py", line 411, in run_test
    return self.test_context.function(self.test)
  File "/usr/local/lib/python3.7/dist-packages/ducktape/mark/_mark.py", line 438, in wrapper
    return functools.partial(f, *args, **kwargs)(*w_args, **w_kwargs)
  File "/opt/kafka-dev/tests/kafkatest/tests/tools/replica_verification_test.py", line 76, in test_replica_lags
    self.start_kafka(security_protocol, security_protocol)
  File "/opt/kafka-dev/tests/kafkatest/tests/tools/replica_verification_test.py", line 52, in start_kafka
    self.kafka.start()
  File "/opt/kafka-dev/tests/kafkatest/services/kafka/kafka.py", line 668, in start
    self.wait_for_start(node, monitor, timeout_sec)
  File "/opt/kafka-dev/tests/kafkatest/services/kafka/kafka.py", line 930, in wait_for_start
    err_msg="Kafka server didn't finish startup in %d seconds" % timeout_sec)
  File "/usr/local/lib/python3.7/dist-packages/ducktape/cluster/remoteaccount.py", line 754, in wait_until
    allow_fail=True) == 0, **kwargs)
  File "/usr/local/lib/python3.7/dist-packages/ducktape/utils/util.py", line 58, in wait_until
    raise TimeoutError(err_msg() if callable(err_msg) else err_msg) from last_exception
ducktape.errors.TimeoutError: Kafka server didn't finish startup in 60 seconds

[frankvicky]

Hi @chia7712
I have run the test three times with different commits, and they all failed due to Timed out waiting to reach non-zero number of replica lags.

Before this patch:

With this patch on my local machine:

With this patch on Jenkins: