Fix NPE for ConfigureNotificationSettings

The NPE is caused by that we have removed the advanced category from
Notification page for android S design but it still tries to get
category and call setInitialExpandedChildrenCount in onCreate().

Only run the relevant logic on the old design since it’s only used to
expand the advanced category and we don’t need the expand feature
anymore for android S.

Bug: 182237530
Fixes: 182532954
Test: robotest & manual
Change-Id: I96f35fa40221079d5498d9d2fab9c75d64698808