/posts.atom: fix banned posts being visible to Members.

Bug: /posts.atom only hid loli/shota, not banned posts and not unsafe
posts when safe mode was on.

app/views/posts/index.atom.erb

@@ -10,7 +10,7 @@
   <% end %>
   <author><name><%= Danbooru.config.app_name %></name></author>
 
-  <% Danbooru.config.select_posts_visible_to_user(CurrentUser.user, @posts).each do |post| %>
+  <% @posts.select(&:visible?).each do |post| %>
     <entry>
       <title><%= post.presenter.humanized_essential_tag_string %></title>
       <link href="<%= post_url(post) %>" rel="alternate"/>