Remove note about night sky in PhysicalSkyMaterial

A night sky texture has been supported for quite some time now: godotengine#38791 So the instruction to use your own shader for this seems to be outdated.

doc/classes/PhysicalSkyMaterial.xml

@@ -6,7 +6,6 @@
 	<description>
 		The [PhysicalSkyMaterial] uses the Preetham analytic daylight model to draw a sky based on physical properties. This results in a substantially more realistic sky than the [ProceduralSkyMaterial], but it is slightly slower and less flexible.
 		The [PhysicalSkyMaterial] only supports one sun. The color, energy, and direction of the sun are taken from the first [DirectionalLight3D] in the scene tree.
-		As it is based on a daylight model, the sky fades to black as the sunset ends. If you want a full day/night cycle, you will have to add a night sky by converting this to a [ShaderMaterial] and adding a night sky directly into the resulting shader.
 	</description>
 	<tutorials>
 	</tutorials>