Always use default includes when preloading discussion list

Making them explicit causes problems when extensions want to include
something by default (e.g. tags)

src/Api/Actions/Discussions/IndexAction.php

@@ -32,9 +32,9 @@ class IndexAction extends SerializeCollectionAction
         'lastUser' => true,
         'startPost' => false,
         'lastPost' => false,
-        'relevantPosts' => false,
-        'relevantPosts.discussion' => false,
-        'relevantPosts.user' => false
+        'relevantPosts' => true,
+        'relevantPosts.discussion' => true,
+        'relevantPosts.user' => true
     ];
 
     /**