Make more TLObject methods private

Even though raw API is somewhat necessary at times,
these methods should remain implementation details.

telethon/_network/mtprotosender.py

@@ -604,7 +604,7 @@ class MTProtoSender:
         else:
             try:
                 with BinaryReader(rpc_result.body) as reader:
-                    result = state.request.read_result(reader)
+                    result = state.request._read_result(reader)
             except Exception as e:
                 # e.g. TypeNotFoundError, should be propagated to caller
                 if not state.future.cancelled():