DO NOT MERGE Redact SyncService stuff from master

Cherry-pick over from master.
This changes the API surface area, deleting things we aren't releasing.
I'll do the internal clean-up at the same time I do the SyncManager
refactor to sit on top of the TaskManager.
Bug: 14997851

Change-Id: Ieebbbcd3324827098e88b36e45e6e82315a51e65