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/post_appeal.rb

@@ -8,7 +8,6 @@ class PostAppeal < ApplicationRecord
   validates_presence_of :reason
   validate :validate_post_is_inactive
   validate :validate_creator_is_not_limited
-  before_validation :initialize_creator, :on => :create
   validates_uniqueness_of :creator_id, :scope => :post_id, :message => "have already appealed this post"
 
   api_attributes including: [:is_resolved]
@@ -60,10 +59,6 @@ class PostAppeal < ApplicationRecord
     end
   end
 
-  def initialize_creator
-    self.creator_id = CurrentUser.id
-  end
-
   def appeal_count_for_creator
     creator.post_appeals.recent.count
   end