[Sync] Cleanup all tab sync enabling logic now that its on by default.

BUG=none
TEST=


Review URL: https://chromiumcodereview.appspot.com/10443046

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@139462 0039d316-1c4b-4281-b951-d872f2087c98
  SyncManagerTest()
      : sync_notifier_mock_(NULL),
        sync_manager_("Test sync manager"),
        sync_notifier_observer_(NULL),
        update_enabled_types_call_count_(0) {}

  SyncManagerTest()
      : sync_notifier_mock_(NULL),
        sync_manager_("Test sync manager"),
        sync_notifier_observer_(NULL),
        update_enabled_types_call_count_(0) {}
