Refactored USBTether, BluetoothTether and WifiTetherDisable preference controllers to extend TogglePreferenceControllers, since they are all SwitchPreference. Bug: 150634051 Test: UsbTetherPreferenceControllerTest, BluetoothTetherPreferenceControllerTest, WifiTetherDisablePreferenceControllerTest, CodeInspectionTest Change-Id: I3b1d1c4e678c65ced8dd506a87c3c43ed300d64f