QQ: add v8 modules

And tidy up some backwards compatible code that is no longer
needed.

Author: kjnilsson

deps/rabbit/src/rabbit_fifo.erl

@@ -377,24 +377,12 @@ checkout(ConsumerTag, CreditMode, #{} = Meta,
        is_tuple(CreditMode) ->
     Servers = sorted_servers(State0),
     ConsumerId = consumer_id(ConsumerTag),
-    Spec = case rabbit_fifo:is_v4() of
-               true ->
-                   case CreditMode of
-                       {simple_prefetch, 0} ->
-                           {auto, {simple_prefetch,
-                                   ?UNLIMITED_PREFETCH_COUNT}};
-                       _ ->
-                           {auto, CreditMode}
-                   end;
-               false ->
-                   case CreditMode of
-                       {credited, _} ->
-                           {auto, 0, credited};
-                       {simple_prefetch, 0} ->
-                           {auto, ?UNLIMITED_PREFETCH_COUNT, simple_prefetch};
-                       {simple_prefetch, Num} ->
-                           {auto, Num, simple_prefetch}
-                   end
+    Spec = case CreditMode of
+               {simple_prefetch, 0} ->
+                   {auto, {simple_prefetch,
+                           ?UNLIMITED_PREFETCH_COUNT}};
+               _ ->
+                   {auto, CreditMode}
            end,
     Cmd = rabbit_fifo:make_checkout(ConsumerId, Spec, Meta),
     %% ???
@@ -418,19 +406,15 @@ checkout(ConsumerTag, CreditMode, #{} = Meta,
                                         NextMsgId - 1
                                 end
                         end,
-            DeliveryCount = case rabbit_fifo:is_v4() of
-                                true -> credit_api_v2;
-                                false -> {credit_api_v1, 0}
-                            end,
+            DeliveryCount =  credit_api_v2,
             ConsumerKey = maps:get(key, Reply, ConsumerId),
-            SDels = maps:update_with(
-                      ConsumerTag,
-                      fun (C) -> C#consumer{ack = Ack} end,
-                      #consumer{key = ConsumerKey,
-                                last_msg_id = LastMsgId,
-                                ack = Ack,
-                                delivery_count = DeliveryCount},
-                      CDels0),
+            SDels = maps:update_with(ConsumerTag,
+                                     fun (C) -> C#consumer{ack = Ack} end,
+                                     #consumer{key = ConsumerKey,
+                                               last_msg_id = LastMsgId,
+                                               ack = Ack,
+                                               delivery_count = DeliveryCount},
+                                     CDels0),
             {ok, Reply, State0#state{leader = Leader,
                                      consumers = SDels}};
         Err ->