posts: fix paginator not appearing when all posts are hidden.

Fix the paginator not appearing when all posts on the page are hidden,
because of deleted posts, banned artists, censored tags, or non-safe
posts in safe mode. This prevented navigating to the next or previous
page.

app/logical/post_sets/post.rb

@@ -67,12 +67,6 @@ module PostSets
       posts.any? {|x| x.rating == "e"}
     end
 
-    def shown_posts
-      shown_posts = posts.select(&:visible?)
-      shown_posts = shown_posts.reject(&:is_deleted?) unless show_deleted?
-      shown_posts
-    end
-
     def hidden_posts
       posts.reject(&:visible?)
     end