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.
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