HUN: Close RemoteInputView when Home is pressed

CLOSE_SYSTEM_DIALOGS usually dismisses the notification shade,
but that's not the case for HUNs because the shade is not actually
open. However, CLOSE_SYSTEM_DIALOGS will now close the Direct Reply
even with HUNs.

Change-Id: If8e5115e33f93db0f8b4e442331ea3d60fc0c63d
Fixes: 29583313