Remove search and help menu items from toolbar

Based on the Settings UI guideline, both of search and help menu items
will be removed from toolbar on Android S.

Bug: 179332520
Test: visual verified
1) Settings -> System -> Gestures -> System navigation
2) Observe the toolbar and check if search and help icons are existing

Change-Id: I3d71eddffb8876f936cf56858d0604aba7d4ee4b