Make spatial audio Firefox-only

Hopefully explained in comment: we have a heisenbug where we sometimes
lack audio from a certain participant, so this simplifies the audio
path by removing the workaround required to do AEC with spatial audio
on chrome.

src/video-grid/useAudioOutputDevice.ts

@@ -16,6 +16,8 @@ limitations under the License.
 
 import { RefObject, useEffect } from "react";
 
+// Uses setSinkId on an audio output element to set the device it outputs to,
+// where supported by the browser.
 export function useAudioOutputDevice(
   mediaRef: RefObject<MediaElement>,
   audioOutputDevice: string | undefined