Disable toggling wifi tethering in secondary user.

- in previous release, the shortcut widget was for the top level
Hotspot & Tethering settings page. The top level settings has logic to
check whether the page is restricted and remove all preferences and
show a message to tell the user that tethering settings are not
available, and the user will not be able to launch the wifi hotspot
settings page.
- the updated shortcut now launches the wifi hotspot page directly.
The settings does not check for restriction. Copy the logic from the top
level settings to check for restriction and remove all preferences
accordingly.

Change-Id: I76fb7838e2db379f6ffbce7bf14003bccc1b10d3
Fixes: 116642428
Test: make RunSettingsRoboTests