Avoid resetting log flags as this could cause data races with
allocating background threads.

Bug: v8:10315
Change-Id: I7be01ff54e349652f182b944ed3f3366d1239ad7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2421814
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70036}