Remove / re-word some settings for WiFi-only devices.

Bug: 3468248

1. Remove Wireless->Mobile networks
2. Remove Wireless->Tethering and WiFi hotspot
3. Remove Wireless->Wi-Fi Settings->Wi-Fi disconnect policy
4. Re-word Network location summary text to not include "mobile network"

Change-Id: I84a551a1b63591974731029b0d4b90a85e43a716