CookieStore::DeleteCookieAsync appears unused (outside a few tests), so remove it

Change-Id: I8530a8b376f000e075d57ebeb70401b2092456f6
Reviewed-on: https://chromium-review.googlesource.com/c/1456677
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Mohammad Refaat <mrefaat@chromium.org>
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631818}
14 files changed