This reverts commit 3ca64085.

Reason: it does not seem to improve anything (including microbenchmarks
that only do "if (m.has(x)) s += m.get(x);" in a tight loop).

Bug: v8:6410
Change-Id: I025bf885f313ac5e54ca450ae9cff5b4a15b04fd
Reviewed-on: https://chromium-review.googlesource.com/574020Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46952}