Currently MediaWiki carries a composer dependency on kafka-php in production.

It's only used in two places, both unused:

• EventRelayerKafka - an implementation of EventRelayer, which is capable of producing to kafka directly
• KafkaHandler for monolog - capable of producing logs into kafka directly.

Neither of these features were ever used to my knowledge. For both features are are using eventgate in production now.

I propose to drop both classes and kafka-php composer dependency. Not quite sure if these are a part of public MediaWiki interface and needs to go through a deprecation. It's only suggested and in require-dev for testing. It is very highly unlikely it's used by anyone outside of the WMF.