Remove numbering_system and change the type of locale
to reduce memory usage of JSDateTimeFormat

Bug: v8:8066
Change-Id: I8a319e05312ffa62f22a382bf150bbe9b48f5f54
Reviewed-on: https://chromium-review.googlesource.com/1242093
Commit-Queue: Frank Tang <ftang@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56296}