The config was mistakenly switched to Bionic already. We keep it
unspecified now to prepare reimaging the bots.

No-Try: true
Bug: chromium:1199430
Change-Id: Ib09d9abbe890fc891af69b6630bf21be85328196
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2853586
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74222}