refactor(calls): drop the deafen iframe-DOM fallback now that the fork owns it (#209)

CallControl.setSound()/applyScreenshareAudioMuted() no longer poke <audio>.muted
inside the EC frame, and the per-membership re-apply (useCallMemberSoundSync)
is gone: with the pin at 0.25.0-lotus.4 the fork applies deafen and the
screenshare-audio mute through its own renderer, including for late joiners.
Verified headless: deafen set before a second participant joins mutes their
track on arrival; deafen/undeafen leaves the screenshare-audio mute in place.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/CallEmbedProvider.tsx

@@ -34,7 +34,6 @@ import {
   useCallHangupEvent,
   useCallJoined,
   useCallThemeSync,
-  useCallMemberSoundSync,
   useCallStart,
 } from '../hooks/useCallEmbed';
 import { callChatAtom, callEmbedAtom } from '../state/callEmbed';
@@ -673,7 +672,6 @@ function CallUtils({ embed, joined }: { embed: CallEmbed; joined: boolean }) {
   // the mobile in-call chat. Both are gated on `joined`.
   useCallHotkeys(embed, joined);
   useAfkAutoMute(joined ? embed : undefined);
-  useCallMemberSoundSync(embed);
   useCallJoinLeaveSounds(embed);
   useCallThemeSync(embed);
   useCallQuality(embed);