Distance Field AO leaving trail of occlusion shadow where character mesh has been.

When using DFAO and moving around the world a trail will be left behind the where the player has been while PIE/Standalone game is being used. This is cleared when exiting these modes.

**Video attached for demonstration

1. Open UE4 (Rolling ball template works well for this)
2. Enable Generate Distance Fields in Project settings and restart editor (if not already enabled)
3. Add Skylight to the scene and set to movable
4. Change the occlusion tint to a bright color to better see the AO
5. PIE
6. Move close to mesh in spectator pawn mode or using other player character types
7. Should see a trail of AO where the player character has moved.
8. Exit PIE

Results: There is a trail left behind the player character where it has moved when DFAO is enabled.

Expected: There should be no trail left behind where the player has moved.