Refactor new tether settings to remove SharedPreferences

Bluetooth, USB and Wifi Disable tether preferences will turn on/off that
type of tethering interface instantly without storing it into
SharedPreferences. They are listening to TetherEnabler to update their
state.
Refactored to remove dependancy on SharedPreferences.

Bug: 151367756
Test: TetherEnablerTest; BluetoothTetherPreferenceControllerTest;
UsbTetherPreferenceControllerTest;
WifiTetherDisablePreferenceControllerTest; AllInOneSettingsTest;
AllInOneTetherPreferenceControllerTest

Change-Id: Ia6cc60bc4de8f08413beb6d41552a18f6fa6a55b