Fix misleading light occlusion preview

[huwpascoe]

Deletes the preview shape raised in #102160

The preview shape was not fit for purpose

• The fill/line color was both misleading and hard to see
• Couldn't preview how the result is supposed to look
• Designers work with the actual lighting visible anyway
• The selected outline already covers that functionality:
  

[KoBeWi]

Some people might be unhappy with their occluders suddenly becoming invisible. Maybe we should have a property for whether the preview should draw or not.

[huwpascoe]

Some people might be unhappy with their occluders suddenly becoming invisible. Maybe we should have a property for whether the preview should draw or not.

If that's the case then it should be promoted to a viewport overlay, with configurable color in editor settings.

[KoBeWi]

It can be property of the node. We have a couple of editor-only properties, so it's not really a problem.

[clayjohn]

I agree with KoBeWi, we need an indicator to show where occluders are. We just need to make it not look like a shadow.

[Calinou]

Occluders can be displayed as an outline, but at the same time, if we want to only display gizmos for selected nodes, the orange outline already serves that purpose.

In general, following godotengine/godot-proposals#6564, there's been a push to only show gizmos of visual-oriented nodes when the node in question is selected to reduce visual clutter.