[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}