Fix notification rendering by removing leftover test code (#1019)

Author: jmartinesp

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/notification/NotificationMapper.kt

@@ -40,7 +40,6 @@ class NotificationMapper(
         roomId: RoomId,
         notificationItem: NotificationItem
     ): NotificationData {
-        notificationItem.event.use { (it as NotificationEvent.Timeline).event }
         val senderId = UserId(notificationItem.senderInfo.senderId)
         return notificationItem.use { item ->
             NotificationData(