Before, configurations were chosen on clusterfuzz side. This migrates
the choice to the V8 repo, to enable easier changing it and to allow
sharing it between different fuzzers.

NOTRY=true
TBR=sergiyb@chromium.org

Bug: chromium:813833
Change-Id: I9890a36fd6aab171d3e13172fc55b274f189e532
Reviewed-on: https://chromium-review.googlesource.com/927681Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51410}