kafka cache treats non-compacted topics as compacted

[jfallows]

Describe the bug
When replaying messages from a non-compacted Kafka topic, only the most recent message for each distinct key is delivered. This is the correct behavior for compacted Kafka topics, but non-compacted Kafka topics should replay all historical messages by default.

To Reproduce
Steps to reproduce the behavior:

1. Use sse.kafka.fanout from zilla-examples
2. Change topic creation to use cleanup.policy delete instead of compacted
3. Follow remaining instructions
4. See only latest message delivered

Expected behavior
Expect all historical messages to be delivered