Remove CQv1

Starting from this commit it is no longer possible to
convert data from CQv1 to CQv2. All data is expected
to use CQv2.

Author: lhoguin

deps/rabbit/src/rabbit_classic_queue_index_v2.erl

@@ -147,8 +147,8 @@ info(#qs{ write_buffer = WriteBuffer }) ->
 
 %% @todo I think we can disable the old message store at the same
 %%       place where we create MsgId. If many queues receive the
-%%       message, then we create an MsgId. If not, we don't. But
-%%       we can only do this after removing support for v1.
+%%       message, then we create an MsgId. If not, we don't until
+%%       strictly necessary (large messages).
 write(SeqId, Msg, Props, State0 = #qs{ write_buffer = WriteBuffer0,
                                        write_buffer_size = WriteBufferSize }) ->
     ?DEBUG("~0p ~0p ~0p ~0p", [SeqId, Msg, Props, State0]),

deps/rabbit/src/rabbit_classic_queue_store_v2.erl

@@ -31,6 +31,7 @@
 
 -spec start_link() -> rabbit_types:ok_pid_or_error().
 
+%% @todo Serial can be in persistent_term instead of process.
 start_link() ->
     gen_server:start_link({local, ?SERVER}, ?MODULE,
                           [update_disk_serial()], []).