Simplify event context menu open

There's no reason to pass the author from QML to C++, we can query the author in the backend

src/app/roommanager.h

@@ -222,8 +222,7 @@ public:
     /**
      * @brief Show a context menu for the given event.
      */
-    Q_INVOKABLE void
-    viewEventMenu(const QString &eventId, NeoChatRoom *room, NeochatRoomMember *sender, const QString &selectedText = {}, const QString &hoveredLink = {});
+    Q_INVOKABLE void viewEventMenu(const QString &eventId, NeoChatRoom *room, const QString &selectedText = {}, const QString &hoveredLink = {});
 
     /**
      * @brief Set a URL to be loaded as the initial room.