Do not use synchronous ConnectivityManager APIs

These have race conditions when used in conjunction with the async
callbacks. Instead, use a default network callback to decide if the
default network is a trusted, validated wifi network

Fixes: 391153635
Test: atest NotificationManagerServiceTest
Flag: android.app.redact_sensitive_content_notifications_on_lockscreen
Change-Id: Idd2dd4fa6ba9a5e0d0b92153c1a22bc0e35620bd