Boot steps: depend on pre_flight, do not enable anything

There are no boot steps that might depend on the one
defined by this plugin.

References rabbitmq/rabbitmq-server#13394.

Closes #298

Author: michaelklishin

src/rabbit_delayed_message.erl

@@ -18,8 +18,7 @@
                    [{description, "exchange delayed message mnesia setup"},
                     {mfa, {?MODULE, setup_mnesia, []}},
                     {cleanup, {?MODULE, disable_plugin, []}},
-                    {requires, external_infrastructure},
-                    {enables, rabbit_registry}]}).
+                    {requires, pre_flight}]}).
 
 -behaviour(gen_server).
 

src/rabbit_delayed_message_sup.erl

@@ -20,8 +20,7 @@
 -rabbit_boot_step({rabbit_delayed_message_supervisor,
                    [{description, "delayed message sup"},
                     {mfa,         {rabbit_sup, start_child, [?MODULE]}},
-                    {requires,    kernel_ready},
-                    {enables,     rabbit_exchange_type_delayed_message},
+                    {requires,    pre_flight},
                     {cleanup,     {?MODULE, stop, []}}]}).
 
 start_link() ->