chore(emqx_connection): delete stale code

src/emqx_connection.erl

@@ -465,62 +465,6 @@ system_continue(Parent, _Debug, State) ->
 system_terminate(Reason, _Parent, _Debug, State) ->
     terminate(Reason, State).
 
-system_code_change(State, _Mod, {down, Vsn}, _Extra)
-    when Vsn == "4.2.0";
-         Vsn == "4.2.1" ->
-    Channel = State#state.channel,
-    NSerialize = emqx_frame:serialize_fun(State#state.serialize),
-    case {State#state.parse_state, element(10, Channel)} of
-        {{none, _}, undefined} ->
-            {ok, State#state{serialize = NSerialize}};
-        {Ps, Quota} ->
-            %% BACKW: e4.2.0-e4.2.1
-            %% We can't recover/reconstruct anonymous function state for
-            %% Parser or Quota consumer. So just close it.
-            ?LOG(error, "Unsupport downgrade connection ~0p, peername: ~0p."
-              " Due to it have an incomplete frame or unsafed quota counter,"
-              " parser_state: ~0p, quota: ~0p."
-              " Force close it now!!!", [self(), State#state.peername, Ps, Quota]),
-            self() ! {close, unsupported_downgrade_connection_state},
-            {ok, State#state{serialize = NSerialize}}
-    end;
-
-system_code_change(State, _Mod, Vsn, _Extra)
-    when Vsn == "4.2.0";
-         Vsn == "4.2.1" ->
-    Channel = State#state.channel,
-    NChannel =
-        case element(10, Channel) of
-            undefined -> Channel;
-            Quoter ->
-                Zone = element(2, Quoter),
-                Cks = element(3, Quoter),
-                NCks = [case Name == overall_messages_routing of
-                            true -> Ck#{consumer => Zone};
-                            _ -> Ck
-                        end || Ck = #{name := Name} <- Cks],
-                setelement(10, Channel, setelement(3, Quoter, NCks))
-        end,
-
-    NParseState =
-        case State#state.parse_state of
-            Ps = {none, _} ->  Ps;
-            Ps when is_function(Ps) ->
-                case erlang:fun_info(Ps, env) of
-                    {_, [Hdr, Opts]} ->
-                        {{len, #{hdr => Hdr, len => {1, 0}}}, Opts};
-                    {_, [Bin, Hdr, Len, Opts]} when is_binary(Bin) ->
-                        {{body, #{hdr => Hdr, len => Len, rest => Bin}}, Opts};
-                    {_, [Hdr, Multip, Len, Opts]} ->
-                        {{len, #{hdr => Hdr, len => {Multip, Len}}}, Opts}
-                end
-        end,
-
-    {_, [Ver, MaxSize]} = erlang:fun_info(State#state.serialize, env),
-    NSerialize = #{version => Ver, max_size => MaxSize},
-
-    {ok, State#state{channel = NChannel, parse_state = NParseState, serialize = NSerialize}};
-
 system_code_change(State, _Mod, _OldVsn, _Extra) ->
     {ok, State}.