models: remove belongs_to_creator macro.

The belongs_to_creator macro was used to initialize the creator_id field
to the CurrentUser. This made tests complicated because it meant you had
to create and set the current user every time you wanted to create an
object, when lead to the current user being set over and over again. It
also meant you had to constantly be aware of what the CurrentUser was in
many different contexts, which was often confusing. Setting creators
explicitly simplifies everything greatly.

app/models/forum_post.rb

@@ -2,7 +2,7 @@ class ForumPost < ApplicationRecord
   include Mentionable
 
   attr_readonly :topic_id
-  belongs_to_creator
+  belongs_to :creator, class_name: "User"
   belongs_to_updater
   belongs_to :topic, :class_name => "ForumTopic"
   has_many :dtext_links, as: :model, dependent: :destroy
@@ -113,7 +113,7 @@ class ForumPost < ApplicationRecord
   end
 
   def validate_topic_is_unlocked
-    return if CurrentUser.is_moderator?
+    return if creator.is_moderator?
     return if topic.nil?
 
     if topic.is_locked?
@@ -139,7 +139,7 @@ class ForumPost < ApplicationRecord
   def update_topic_updated_at_on_create
     if topic
       # need to do this to bypass the topic's original post from getting touched
-      ForumTopic.where(:id => topic.id).update_all(["updater_id = ?, response_count = response_count + 1, updated_at = ?", CurrentUser.id, Time.now])
+      ForumTopic.where(:id => topic.id).update_all(["updater_id = ?, response_count = response_count + 1, updated_at = ?", creator.id, Time.now])
       topic.response_count += 1
     end
   end