If the lxd/lxc knows about the bridge (i.e. it's managed) then run the following:

```bash
lxc network delete lxdbr0
```

If it's no longer managed by lxd/lxc, you need to run the following commands:

```bash
ip link set lxdbr0 down
ip link delete lxdbr0 type bridge
```

You may need to kill the LXD process listening on port `8443` (it requires sudo as lxd runs as root)

```bash
sudo lsof -i :8443
```