Fix DQT in definition export (redundant property)

The correct place for the `default_queue_type` property
is inside the `metadata` block. However, right now we'd
always export the value outside of `metadata` AND only
export it inside `metadata`, if it was not `undefined`.

This value outside of `metadata` was just misleading:
if a user exported the definitins from a fresh node,
changed `classic` to `quorum` and imported such modified
values, the DQT would still be `classic`, because RMQ looks
for the value inside `metadata`. Just to make it more confusing,
if the DQT was changed successfully one way or another, the
value outside of `metadata` would reflect that
(it always shows the correct value, but is ignored on import).

(cherry picked from commit 73da2a3fbb)

deps/rabbit/src/rabbit_definitions.erl

@@ -1081,12 +1081,10 @@ list_vhosts() ->
 
 vhost_definition(VHost) ->
     Name = vhost:get_name(VHost),
-    DQT = rabbit_queue_type:short_alias_of(rabbit_vhost:default_queue_type(Name)),
     #{
         <<"name">> => Name,
         <<"limits">> => vhost:get_limits(VHost),
-        <<"metadata">> => vhost:get_metadata(VHost),
-        <<"default_queue_type">> => DQT
+        <<"metadata">> => vhost:get_metadata(VHost)
     }.
 
 list_users() ->