Disconnected bluetooth sensors are shown in wasm/mqtt

[blammit]

Go to I/O > Bluetooth sensors. Observe that Bluetooth sensors that are offline are still connected.

This is due to fixes for #1666; see the discussion there.

This can be reproduced by opening gui-v2 via wasm, waiting until it is idle for a while, and coming back; or by forcing a disconnect at the MQTT level. At this point, the Bluetooth devices are offline, and should disappear from the model.