Partially revert "Implement perfect forward secrecy for MTProto (#4618)"

This partially reverts commit 5a3a94eb51.
It should be re-introduced once the rest of comments are addressed.

Session changes are kept for the future, even if unused for now,
as there may be people who have already upgraded their session.

telethon/network/requeststate.py

@@ -10,9 +10,9 @@ class RequestState:
     """
     __slots__ = ('container_id', 'msg_id', 'request', 'data', 'future', 'after')
 
-    def __init__(self, request, after=None, msg_id=None):
+    def __init__(self, request, after=None):
         self.container_id = None
-        self.msg_id = msg_id
+        self.msg_id = None
         self.request = request
         self.data = bytes(request)
         self.future = asyncio.Future()