SystemUi: Nuke secondaryIcon.

  bb4a702e introduced a secondary icon that would allow
  for the manipulation of the ringer stream during specific
  active stream types.

  This duplicates functionality with our expandable volume panel
  and is not as effective as a utility, so kill it with fire.

Change-Id: Ia74fc95a3886f4c57b8e632b7b26f7ade4247e41