Drop dead sendWhisperGroupMessage — composer never existed

IRoomSession.sendWhisperGroupMessage(userId) was declared in the
interface and implemented in RoomSession by sending 'new
ChatWhisperGroupComposer(userId)' — but no such composer class
exists in the renderer (the file was never created). The only
whisper composer is RoomUnitChatWhisperComposer, which takes
(recipientName, message, styleId), not a userId.

No client call site references sendWhisperGroupMessage (grep across
Nitro-V3/src returned zero hits). Removing the dead interface method
+ broken impl is safer than inventing a ChatWhisperGroupComposer
class with no server-side handler.

packages/api/src/nitro/session/IRoomSession.ts

@@ -21,7 +21,6 @@ export interface IRoomSession
     sendPostureMessage(posture: number): void;
     sendDoorbellApprovalMessage(userName: string, flag: boolean): void;
     sendAmbassadorAlertMessage(userId: number): void;
-	sendWhisperGroupMessage(userId: number): void;
     sendKickMessage(userId: number): void;
     sendMuteMessage(userId: number, minutes: number): void;
     sendBanMessage(userId: number, type: string): void;