create rake task to remove preview bulletins

lib/tasks/bulletin_tasks.rake

@@ -1,4 +1,8 @@
-# desc "Explaining what the task does"
-# task :bulletin do
-#   # Task goes here
-# end
+desc 'Remove duplicated bulletins (announcements) created by preview'
+
+namespace :bulletin do
+  task :remove_preview_bulletins do
+    bulletins = Bulletin.where(is_preview: true)
+    bulletins.destroy_all
+  end
+end