searchable: refactor searchable_includes.

Pass searchable associations directly to search_attributes instead of
defining them separately in searchable_includes.

app/models/forum_post_vote.rb

@@ -19,7 +19,7 @@ class ForumPostVote < ApplicationRecord
   end
 
   def self.search(params)
-    q = search_attributes(params, :id, :created_at, :updated_at, :score)
+    q = search_attributes(params, :id, :created_at, :updated_at, :score, :creator, :forum_post)
     q = q.forum_post_matches(params[:forum_post])
     q.apply_default_order(params)
   end
@@ -58,10 +58,6 @@ class ForumPostVote < ApplicationRecord
     end
   end
 
-  def self.searchable_includes
-    [:creator, :forum_post]
-  end
-
   def self.available_includes
     [:creator, :forum_post]
   end