remove Kafka eight module

[b-slim]

I think this module is not used anymore (am not sure if it was really used), it has some outdated dependencies and takes out build resources for no reason.
Am suggestion removing it.

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This change is 

[b-slim]

CC @fjy

[freakyzoidberg]

Hello, although we wouldn't be impacted by this removal,
We use a slightly modified version of this for Kafka 10, which I guess we could contribute back if you want.

[b-slim]

@freakyzoidberg contribution is more than welcome, you want to send a PR to add your module as part of contrib modules?

[nishantmonu51]

LGTM, 👍

[jihoonson]

Please check the CI failure.

[jon-wei]

[ERROR] Failed to execute goal on project druid-integration-tests: Could not resolve dependencies for project io.druid:druid-integration-tests:jar:0.13.0-SNAPSHOT: Could not find artifact io.druid.extensions:druid-kafka-eight:jar:0.13.0-SNAPSHOT in sonatype-snapshots (https://oss.sonatype.org/content/repositories/snapshots/) -> [Help 1]

Looks like the dependency needs to be removed from druid-integration-tests as well

[jon-wei]

I'm not sure if we should remove this (or maybe keep those firehose implementations in sync with the kafka version used by kafka-indexing-service, is that worth the effort?).

If we do get rid of it, we should probably also remove http://druid.io/docs/latest/development/extensions-contrib/kafka-simple.html and take out the docs for both extensions as well

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