/var/run/log/rhttpproxy.log
<DATE> In(###) Rhttpproxy[#######]: [Originator@####sub=Default] [PacketCapture] Removing pcap files last modified before: <DATE>
The cleanup will happen when rhttp service is restarted, upon ESXi system boot or the tmp.json if it's created and configured per the following link. See Collecting network packets using the lightweight PacketCapture on ESXi.
This is working as designed.