Make `submissions_canceled` and `add_chunks_done_to_submissions_failed` migrations bidirectional

[Qqwy]

Most of the migrations have both a .up.sql and a .down.sql.

However, it seems like we missed this in three recent PRs

• Support cancelling a submission #75
• Add chunks_done field to submissions_failed #108
• Drop: Unused chunks_metadata table #123

Making those migrations reversible is only a couple of minutes of work, so I think it would be good to do so.

• Check this in CI so the wrong command is no longer used.