Delete obsoleted setting

example.config.toml

 # All other incoming connections are going to be dropped.
 concurrency = 8192
 
-# A size of user-space buffer for TCP to use. Since we do 2 connections,
-# then we have tcp-buffer * (4 + 2) per each connection: read/write for
-# each connection + 2 copy buffers to pump the data between sockets.
-#
-# Deprecated: this setting is no longer makes any effect.
-# tcp-buffer = "4kb"
-
 # Sometimes you want to enforce mtg to use some types of
 # IP connectivity to Telegram. We have 4 modes:
 #   - prefer-ipv6: