Remove automatic adding of adb into default.prop

Default.prop can interfere with UsbDeviceManager's management of usb state.
Adb is now enabled for userdebug and eng builds directly from UsbDeviceManager.

Bug: 31814300
Test: Manually verified that logcat is not kicked
Change-Id: I69c998c0dd184f9440cc236d82cc2f25f36e8734