Is it possible to filter metrics on the Heavy Forwarder so they don't get passed along? Either a whitelist approach or blacklist approach is fine.
There are lots of ways to skin a cat. I suggest you start by looking here:
https://docs.splunk.com/Documentation/SplunkCloud/8.0.0/Forwarding/Routeandfilterdatad
Come back if you have any further questions or want further explanations.