StatusBarSettings: Fix NW traffic not being properly hidden from search

On devices with notches (those that obviously set the overlay config),
the network traffic monitor preference can still appear in settings
search results. Fix this by not depending on whether the user has ever
opened status bar settings. Additionally turn the static boolean variable
into non-static since it no longer makes sense.

Change-Id: I7d4ed3d8fc84949a67e6d5f98c9a6e8719385ab0