fixup! Add docs and restrict deleting to non-lobby and read-write chats

docs/chat.md

@@ -119,7 +119,9 @@ Base endpoint is: `/ocs/v2.php/apps/spreed/api/v1`
         `X-Chat-Last-Common-Read` | int | ID of the last message read by every user that has read privacy set to public. When the user themself has it set to private the value the header is not set (only available with `chat-read-status` capability)
 
     - Data:
-        TODO
+        The full message array of the new system message "You deleted a message", as defined in [Receive chat messages of a conversation](#receive-chat-messages-of-a-conversation)
+        The parent message is the object of the deleted message with the replaced text "Message deleted by you".
+        This message should not be displayed to the user but instead be used to remove the original message from any cache/storage of the device.
 
 
 ## Mark chat as read