For efficiency, we store the list of PreCQ build configs in CIDB and only recompute them when a new CL revision is uploaded. However, outdated configs can potentially hang around for a very long time.

This surfaced recently when we removed a config, and for weeks engineers had trouble getting CLs through the PreCQ, despite a PSA saying that a CL rebase would resolve the issue.

In a perfect world, we would recompute the build configs to use after a reasonable delay (1 week?). This would also fix a problem in which existing CLs never run new PreCQ builders after they are added.

For the short term, we need some way to manually purge the x86-alex builder from existing CLs.