Use primary user's LOCK_SCREEN_SHOW_NOTIFICATIONS.

Only primary user can set LOCK_SCREEN_SHOW_NOTIFICATIONS,
profile can only set notifications to be redacted. When the
user changes notification settings for a work app, this class
is invoked from the profile, meaning it attempts to read
LOCK_SCREEN_SHOW_NOTIFICATIONS for the profile, which is not
there. As a result the function always returs 0 for work apps.

Bug: 111112011
Test: atest packages/apps/Settings/tests/robotests/src/com/android/settings/notification/VisibilityPreferenceControllerTest.java
Change-Id: Ifb50209ea8ea8fb6639f00ca8b7cf8a4295890ad
(cherry picked from commit f14de789)