`downloadMedia` exists because a widget's client cannot fetch media: it
has no access token, and its only route to a file is MSC4039 over the
widget API. A component host hands over a client that does hold
credentials, so Element Call fetches media with it and the callback was
never needed there. It comes off `ElementCallHostBridge`, leaving a host
with only what it must understand, and stays on the internal HostBridge
for the widget.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>