DeskClock: Fix RingtonePicker

* At the moment, there is an additional spacing between the header
  and the content, that will move up with the collapsing toolbar
  but stay there for the content to scroll below it
* This is caused by the ringtone_picker layout leaving space for the
  system status bar, which the collapsing toolbar already does
* Remove fitsSystemWindows

Change-Id: I4e96d3da323c57ff94c53b47119a695987c4c3e3