Updating SIAB when deleting a track from SCA admin

[Adam Collard]

When deleting tracks from SCA's admin interface, we should make sure that SIAB is updated properly.

as per Natalia:

The right thing would be:

1- check that no revision is released to the track being removed, fail if yes;
2- on track delete update snaprevs by cleaning up the entries

[William Grant (wgrant)]

As discussed on IRC, we won't erase the history from snaprevs (neither by removing the rows or setting their revoked flag). Instead we'll act like the channels are closed and set the most recent entries to deleted, which should be easily done using a full channelmap push with delete_omitted.

This will prevent installations but not e.g. upgrades through epochs. If we do desire full history erasure we can set revoked on a case by case basis, and if it becomes common we can look at automating it once the new SCA->snaprevs API is done (likely next cycle).