pixiv_ugoira_frame_data not vailable through API anymore

[nonamethanks]

As mentioned in https://danbooru.donmai.us/forum_topics/16610, the value pixiv_ugoira_frame_data is not accessible through the api anymore. It used to be possible to get it before, and it's still displayed in the HTML, so there's no reason for it not to be available through the api as well, even if only through the "only" api option.