lxc config device remove haproxy http1 would do it. In fact what you ran likely removed the device despite the error. That’s because lxc config device remove can remove multiple devices at once so it tried to remove devices named:
- http1
- proxy
- listen=tcp:0.0.0.0:80
- connect=127.0.0.1:80
The first one likely succeeeded as it’s an actual device, all the others don’t exist, causing the error.