Background threads are not supposed to use any handles, so this
handle scope is not needed.

R=ahaas@chromium.org

Change-Id: I2f4776b897256684205c35633fbe1e1365abab91
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1981151Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65624}