[Sync::USS] Move password sync related classes to /sync sub-folder

Bug: 902349
Change-Id: I565b746737cc1567cf75abf4924c77eb648c3b46
Reviewed-on: https://chromium-review.googlesource.com/c/1322869
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606595}
16 files changed