Does anybody know how to delete messages from topics after consuming them? My source if Kafka.

Might you want to replay those messages again later, in case of a failure or something? That's a feature of Kafka

Yeah, Kafka makes it pretty hard to delete stuff (thought it's not impossible, since version 0.11). If you need to keep another consumer or consumer group updated on your consumer's progress, you should program the other consumer to look up the offsets