Hide following typing preference setting in SuW.

Hide following typing switch preference setting in SuW.

Bug: 214876729
Test: Start set-up wizard > Assistive options > Vision settings >
           Magnification > Following typing preference is invisible
      make RunSettingsRoboTests ROBOTEST_FILTER=
           ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: I4ab64deeef321390c5b89c8ea58ea469fb5c09bf