Remove `post` index from `$wp_post_types['post']`

If I go to `/edit.php` I can still see the list of posts from my browser. Removing the `post` data from the global variable `$wp_post_types` seems to fix this.

More info: https://core.trac.wordpress.org/browser/tags/3.9/src/wp-includes/post.php#L1346