Revert of Enable 'First-Party-Only' cookies by default. (patchset #3 id:40001 of https://codereview.chromium.org/1032063002/)

Reason for revert:
Blink OWNERs would like to wait a bit before shipping: https://groups.google.com/a/chromium.org/d/msg/blink-dev/wKZBCzcNssg/nZ1CFmgddJcJ

Original issue's description:
> Enable 'First-Party-Only' cookies by default.
>
> This patch reverts https://codereview.chromium.org/940373002, and adds
> back in the ~2 lines and tests that are still relevant.
>
> BUG=459154
>
> Committed: https://crrev.com/bdd0b09b5371066ad6d6c0ef2c32f5b92595316d
> Cr-Commit-Position: refs/heads/master@{#322533}

TBR=cbentzel@chromium.org,jochen@chromium.org,rsleevi@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=459154

Review URL: https://codereview.chromium.org/1043403003

Cr-Commit-Position: refs/heads/master@{#323190}
15 files changed