Use rabbit_nodes to list nodes in two plugins

... instead of using an internal implementation.

The plugins are `rabbitmq_peer_discovery_common` and
`rabbitmq_sharding`.

References #7058.

Author: dumbbell

deps/rabbitmq_peer_discovery_common/src/rabbit_peer_discovery_cleanup.erl

@@ -288,13 +288,7 @@ maybe_remove_nodes([Node | Nodes], false) ->
 %%--------------------------------------------------------------------
 -spec unreachable_nodes() -> [node()].
 unreachable_nodes() ->
-    Status = rabbit_mnesia:status(),
-    Nodes = proplists:get_value(nodes, Status, []),
-    Running = proplists:get_value(running_nodes, Status, []),
-    All = lists:merge(proplists:get_value(disc, Nodes, []),
-                      proplists:get_value(ram, Nodes, [])),
-    lists:subtract(All, Running).
-
+    rabbit_nodes:list_unreachable().
 
 %%--------------------------------------------------------------------
 %% @private

deps/rabbitmq_sharding/src/rabbit_sharding_shard.erl

@@ -127,7 +127,4 @@ v(#resource{virtual_host = VHost}) ->
     VHost.
 
 foreach_node(F) ->
-    [F(Node) || Node <- running_nodes()].
-
-running_nodes() ->
-    proplists:get_value(running_nodes, rabbit_mnesia:status(), []).
+    [F(Node) || Node <- rabbit_nodes:list_running()].