On your OSSEC HUB, run:
/var/ossec/bin/agent_control -ln -s | cut -f1 -d, | grep -v na | xargs -I{} /var/ossec/bin/manage_agents -r {}
This will remove all agents that are not currently connected to the HUB
How to Remove Disconnected and Never Connected Agents from the HUB with the CLI
