Don't reset country code once it is persisted

This change simply ignores resetting of country code by cellular
networks to avoid disconnecting existing wifi connections. It also
defers setting newly found country code until after existing Wifi
connection is torn down.

Also removes some dead code related to resetting of country codes.

Bug: 13894807
Change-Id: Ie2fcfdd4b3be8ba94542772c132fb1acb6a2c683