Remove help icon from the toolbar of App info page

On Android S, the help menu will be removed from the toolbar in all
setting pages. This is using a feature flag to turn on/off the help
menu. Then, it should be entirely removed when the collapsing toolbar
feature rolled out.

Bug: 177274632
Test: visual verified
Change-Id: I5aceb9f0a99ecee948272ee584bbebdcce7b7943