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These switches are no longer used by internal testing so they can be
removed. This also removes ExternalAuthUtils' dependency on chrome.

Bug: 1145663
Change-Id: I5ee1468bd78bd9bd7b3b0bf041aed214bb5e6016
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518803Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Liquan (Max) Gu <maxlg@chromium.org>
Commit-Queue: Nick Burris <nburris@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825034}