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The code to migrate sync.local_device_guids to the new
sync.local_device_guids_with_timestamp has been active for 1 year
(crrev.com/1827435), so it can be removed now.

TBR=treib@chromium.org
TBR=droger@chromium.org

Fixed: 994339
Change-Id: If6fed35ada178808a4171d790f51451f5a8192df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464934
Commit-Queue: Victor Vianna <victorvianna@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816117}