Now that sweeping uses its own RememberedSet, pre-freeing of empty
buckets is not necessary anymore. Mutator inserts into a different
remembered set, than the sweeper removes slots from.

Bug: v8:9454
Change-Id: I65d046926aa82aeb9eca7694e6a7eff1331d7e01
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1835547
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64114}