Turn off adb on user builds.

Tungsten is the first device we have done since post_process_props.py
and UsbDeviceManager were added that by default has no services running
on usb. Everything else has mtp.  This makes it so we always populate
the property with something.

Change-Id: Ic24f52462ed8866e87499c715dd21937e5b1128d
1 file changed