Change platform::CreateDefaultPlatform from V8_DEPRECATE_SOON to
V8_DEPRECATED.

Bug: v8:8562
Change-Id: I053ff29b27dcd454960007bfd6597a01e1b2e62a
Reviewed-on: https://chromium-review.googlesource.com/c/1411636Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58831}