Rebuild if a dependency is no longer in the queue

[lazka]

Scenario as happened in msys2/MINGW-packages#11156

• package + rebuilds get added to the queue
• package gets reverted
• rebuild stays and gets added to the repo
• boom

Potential fixes:

• Store the list of dependencies used from the queue alongside the build
• If one of those packages is no longer there, throw out the current build
• Downside: requires extra fetches for every package...

[lazka]

An simpler way might be to delete/ignore all packages uploaded after the removed build. That will lead to more rebuilds, but means we don't have to track dependencies.

• Delete all newer than packages that need to be cleaned during the scheduler (no builds should be active, otherwise this is racy)
• Ignore all packages that are to be deleted in fetch-assets, to they don't end up in stating/the repo.

[lazka]

Another problem is a dependency cycle that is finished and the wrong package gets updated/deleted, resulting in the wrong build order, since one of them is already in staging.

[lazka]

Another option is to fail and require for some manual input to continue (either delete deps, or continue as now)