Show restricted message in Wi-Fi hotspot settings

- Remove Wi-Fi hotspot preferences in settings search if Wi-Fi hotspot is disallowed

- See the result screenshot in b/203168953#comment12

Bug: 203168953
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=WifiTetherSettingsTest

Change-Id: Id4416fd0659b596e4e6f31890a139198219f4552