Reland "[iOS] Removing ChromeIdentityBrowserOpener protocol"

This is a reland of df892dc3

This patch needs to land after crrev.com/i/4047385

Original change's description:
> [iOS] Removing ChromeIdentityBrowserOpener protocol
>
> ChromeIdentityBrowserOpener is not used anymore.
>
> Change-Id: I07e3f28ca24db2c21c595814a3972cd6bbcc7407
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3089116


> Commit-Queue: Jérôme <jlebel@chromium.org>
> Commit-Queue: Javier Flores <javierrobles@chromium.org>
> Auto-Submit: Jérôme <jlebel@chromium.org>
> Reviewed-by: Javier Flores <javierrobles@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#910808}

Change-Id: If7b2453284e97cefc58bff7039ad3af30d12b7f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3086454


Reviewed-by: Javier Flores <javierrobles@chromium.org>
Commit-Queue: Jérôme <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#911212}