Remove the 3D camera gizmo icon

[Calinou]

master version of #49644.

The gizmo icon obstructed the line-based camera gizmo, which made it difficult to see the actual camera orientation.

This also removes the unused SpatialStreamPlayer gizmo icon.

This closes godotengine/godot-proposals#425.

Preview

Before

After

[Zireael07]

I don't think it's a move in the right direction. The gizmo should rotate to show the correct direction and/or have a direction arrow added. The pink camera extents gizmo can get very small for small fov cameras and/or zoomed out view.

[Calinou]

@Zireael07 The gizmo icon can't be made to rotate in all situations. For instance, if you're right in front or behind the camera, it would spazz out in various directions.

It can be done when you look at the camera from other directions, but it might not be trivial.

We could perhaps add a solid box to complement the pink gizmo as proposed in godotengine/godot-proposals#425, but I'd rather not see a complex model added just for this.

[aaronfranke]

What about if the gizmo icon behaved like a two-sided Sprite3D?

[akien-mga]

I'm also slightly concerned about readability, we might end up with situations where the camera is hard to locate.

But I agree that removing the billboarded icon is good, further improvements should be made on the 3D gizmo itself to make it more readable (e.g. changing scale, colors, or adding a triangle showing the up direction as done in Blender).

[akien-mga]

Thanks!

[Calinou]

adding a triangle showing the up direction as done in Blender).

There's already one (you can see it on the screenshot), but maybe it needs to be drawn differently to be easier to notice.