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This is a reland of 1180542b

The internal CL is rolled in now. Let's try again...

Original change's description:
> Remove BlockThirdPartyCookies preference
>
> The boolean BlockThirdPartyCookies preference was replaced by
> CookieControlsMode enum. Existing settings were migrated since M83.
> Since all usage of the preference has been removed, the preference
> can be removed and existing settings cleared.
>
> Bug: 1104836
> Change-Id: Ie6e38b0a424981395c627459d684030ea84a58b7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2387805
> Reviewed-by: Balazs Engedy <engedy@chromium.org>
> Reviewed-by: Gabriel Charette <gab@chromium.org>
> Commit-Queue: Christian Dullweber <dullweber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#803844}

Tbr: engedy@chromium.org, gab@chromium.org
Bug: 1104836, 1124326
Change-Id: Iebe3205beb4426cda5305eb7c69eb4e575df2cfc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391073Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804298}