Now that background threads participate in sweeping, this method
races because multiple threads now want to update that counter. We could
either make this counter atomic or remove it entirely. This CL removes
this counter since it isn't strictly necessary, it is only used when
sweeper finds more garbage than markers. This happens e.g. with
right-trimming but should be rare and is eventually fixed in the next
GC.

Bug: v8:10315
Change-Id: Iebae8937860160a3b49bedd03c2e21e41f7dfe76
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2349296Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69334}