Remove ConsumerRebalanceProtocolTests

These tests were just verifying Kafka’s own rebalance protocol, not anything specific
in Spring for Apache Kafka framework. Since the new protocol is handled entirely by the
Kafka server, there’s no need to test it here. Users can enable the protocol via the
config - group.protocol. No extra framework logic involved.

Testing the protocol in the framework test suite is unnecessary and leads to long-running
tests without added value.

See the ref docs here:
https://docs.spring.io/spring-kafka/reference/4.0/kafka/receiving-messages/rebalance-listeners.html#new-rebalalcne-protocol

Signed-off-by: Soby Chacko <[email protected]>

Author: sobychacko