API: remove various associated fields included by default.

Remove various associated fields that were included by default on
certain endpoints. API users can use the only param to include the
full association if they need these fields.

* /artists.json: urls.
* /artist_urls.json: artist.
* /comments.json: creator_name and updater_name.
* /notes.json: creator_name.
* /pools.json: creator_name.
* /posts.json: uploader_name, children_ids, pixiv_ugoira_frame_data.
* /post_appeals.json: is_resolved.
* /post_versions.json: updater_name.
* /uploads.json: uploader_name.

app/models/pool.rb

@@ -15,7 +15,7 @@ class Pool < ApplicationRecord
   after_save :create_version
   after_create :synchronize!
 
-  api_attributes including: [:creator_name, :post_count]
+  api_attributes including: [:post_count]
 
   module SearchMethods
     def deleted
@@ -279,10 +279,6 @@ class Pool < ApplicationRecord
     (post_count / CurrentUser.user.per_page.to_f).ceil
   end
 
-  def creator_name
-    creator.name
-  end
-
   def validate_name
     case name
     when /\A(any|none|series|collection)\z/i