Marking the labels as unused is only needed when we abort code
generation. Otherwise the DCHECKs in the label destructors are useful to
catch bugs.

R=jgruber@chromium.org

Bug: v8:12244
Change-Id: I63198f98a7acd1f2528d31964c01bc6815ba99a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3205899
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77267}