Move flood control from core to API layer

This means that flood control can be disabled depending on the nature of the request (i.e. when authenticated using a master API key). The particular use case for this is to allow using the API to migrate data from an old forum.

src/Core/CoreServiceProvider.php

@@ -95,7 +95,6 @@ class CoreServiceProvider extends AbstractServiceProvider
         $events->subscribe('Flarum\Core\Listener\UserMetadataUpdater');
         $events->subscribe('Flarum\Core\Listener\EmailConfirmationMailer');
         $events->subscribe('Flarum\Core\Listener\DiscussionRenamedNotifier');
-        $events->subscribe('Flarum\Core\Listener\FloodController');
 
         $events->subscribe('Flarum\Core\Access\DiscussionPolicy');
         $events->subscribe('Flarum\Core\Access\GroupPolicy');