Remove KidsModeTaskOrganizer

To prevent app content from being obscured by navigation bar forcibly
shown in Kids Space, DisplayPolicy sets mForceConsumeSystemBars to true.
With that, we don't need KidsModeTaskOrganizer anymore.

Fix: 285036830
Fix: 283317142
Fix: 270458958
Test: Rotate the device in the home screen of Kids Space. See if the
      home screen layout matches the current orientation.
Test: Exit Kids Space and make sure the device doesn't crash.
Change-Id: I7b81b161f3de8cfdc288934acb75d233523b1c9a