Remove the last remaining uses of the PixivUgoiraFrameData model. As of
32bfb8407, Ugoira frame data is now stored in the MediaMetadata model,
under the `Ugoira:FrameDelays` EXIF field.
The pixiv_ugoira_frame_data table still exists, but it can be removed
after this commit is deployed.
Fixes#5264: Error when replacing with ugoira.
Bug: When uploading a direct Pixiv image URL, we ignored it in favor of the
image URL returned by the Pixiv API. This meant if you tried to upload the
original version of a revised image, we would get the revised version instead.
Fix: When given a direct Pixiv image URL, use it as-is if it's a full
image URL. If it's a sample image URL, ignore it in favor of the full image
URL as returned by the API, unless the post is deleted and the API data
is unavailable.
