[Sb] Don't add NetworkControllerImpl as a demo mode callback

This class is already unused in the display of networking icons in the
status bar and quick settings. Furthermore, there is an infinite loop
bug that gets triggered if using `-e slot N`, where N > 1, in a demo
command.

Until we can fully remove the class, we can just remove it as a demo
mode listener.

Test: manual via demo mode
Test: adb shell -n dumpsys activity service com.android.systemui/.dump.SystemUIAuxiliaryDumpService and check for
NetworkControllerImpl as a listener
Bug: 336357360
Flag: NONE

Change-Id: I743fb7555e04738e8da51951fb3cf7ec75bf6cb3