YouTube urls cannot be removed from charts in the editor #419
Description
BOT
Youtube urls cannot be removed from the "Edit Song Data" tab anymore and under certain circumstances, the migration will fail to remove the value, preventing the chart from using manually provided media. The specific edge case I ran into involves updating a song where I do not have the media downloaded and the youtube video fails to download. I downloaded a mirror of the video and manually added it to the chart, but I cannot open the song in the editor as it still prompts to download it from youtube, which fails. Migrating the song says it succeeds, but it does not remove the youtube video keys. In order to fix it, I have to manually edit the song.json.
I propose that either the youtube url field should still be shown to the user in the "Edit Song Data" UI when its value isn't null, so that it can be manually removed or modified to a new url by the user if necessary. Or, the migration tool should wipe out the video url and set it to the preview url even when the video data isn't on disk, so the user can manually attach media.