Do not need a function to provide fallback value with default defined in config.exs

lib/pleroma/web/mastodon_api/views/instance_view.ex

@@ -23,7 +23,7 @@ def render("show.json", _) do
         streaming_api: Pleroma.Web.Endpoint.websocket_url()
       },
       stats: Pleroma.Stats.get_stats(),
-      thumbnail: instance_thumbnail(),
+      thumbnail: Keyword.get(instance, :instance_thumbnail),
       languages: ["en"],
       registrations: Keyword.get(instance, :registrations_open),
       # Extra (not present in Mastodon):
@@ -88,9 +88,4 @@ def federation do
     end
     |> Map.put(:enabled, Config.get([:instance, :federating]))
   end
-
-  defp instance_thumbnail do
-    Pleroma.Config.get([:instance, :instance_thumbnail]) ||
-      "#{Pleroma.Web.base_url()}/instance/thumbnail.jpeg"
-  end
 end