Trust: Request removal of the notification when disabling the preference

* Right now, nothing requests the removal of the notification
* This means, that disabling the preference still leaves us with the
  notification
* By notifying the service of the user action, the notification gets
  cancelled properly

Change-Id: I26d23f3dde582dbc923faaa558d5f0bf00d49035
(cherry picked from commit 706da809)