Fix NPE in WirelessSettings.onCreate() for SDK and non-BT devices.

Fix NPE when entering Settings app in the SDK (and for devices without
Bluetooth). Also remove the "Bluetooth settings" item in addition to
the Bluetooth toggle item from Wireless settings when BT is missing.

Bug: 4149307
Change-Id: Iecc5960a193cf88664d3217b4d7bdbc2276dabc0