All post types get numbers

Decided this is necessary because some notifications will need to link
to posts which are not comments (e.g. a “renamed” post)

src/Core/Models/CommentPost.php

@@ -15,22 +15,6 @@ class CommentPost extends Post
      */
     protected static $formatter;
 
-    /**
-     * Add an event listener to set the post's number, and update the
-     * discussion's number index, when inserting a post.
-     *
-     * @return void
-     */
-    public static function boot()
-    {
-        parent::boot();
-
-        static::creating(function ($post) {
-            $post->number = ++$post->discussion->number_index;
-            $post->discussion->save();
-        });
-    }
-
     /**
      * Create a new instance in reply to a discussion.
      *