Include user profiles when calculating areChannelsBypassingDnd

This also means we need to syncChannelsBypassingDnd() whenever users are removed, in case the removed user was a profile of the current one.

(Also some minor cleanup in PreferencesHelper -- dead code related to invalid shortcuts -- and PreferencesHelperTest).

Fixes: 291874057
Test: atest PreferencesHelperTest
Change-Id: I87e9a1c62a90bdcbad42ea8abfa4db87f706ea15