Delete topics from topic registry over Kafka instead of the ingest service

[raminqaf]

This is a follow-up issue of #155. Currently, we are deleting the Kafka topics in the topic registry using the IngestService over an IngestClient. The deletion job in the mirror sets the X_API_KEY in its environment variable and uses this variable to authenticate itself with the ingest service.
We should remove this logic and directly use the Producer API to ingest the proper key with a null value in the topic registry.