Deprecate the Cookie Sync Manager

The CookieSyncManager is largely useless as the WebView
automatically syncs cookies every 30s (whether you like it
or not). The one method which needs to be saved is sync,
there is no other way to force a sync without this.
We move sync to the CookieManager and rename it to flush
for greater consistency.

Bug: 11060034
Change-Id: I8a14998020eea54f196fc6ed845b09ed69cfd447