Fix Connected devices page UI not update after paired

This CL before, onChanged(null) will cause PreferenceGroup
didn't update UI in ConnectedDeviceDashboardFragment.

This CL remove onChanged(null) and set unvisible of SliceView
in the constructor.

Bug: 142220754
Test: make -j42 RunSettingsRoboTests
Change-Id: Ib20db373430589c5c5efbe8a4c866b7fae4f3399
2 files changed