This reverts commit 0d2ed6c3.

The CL introduced perf regressions: crbug.com/735649.

We are going to reland the CL in an isolated V8 roll to ensure
that perf regressions are attributed correctly.

Original commit message:
> [heap] Allow a minimum semi-space size of 512K.
> This CL also reduces the minimum semi-space size to 512K.
> BUG=chromium:716032

BUG=chromium:735649

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I1f1b08ca6853347c00070f000c309d839ff8a4bb
Reviewed-on: https://chromium-review.googlesource.com/552541Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46349}