Cycles: Remove Westin closure.

Was hooked up last year for testing purposes, as we already had some code for it, but the closure itself is not really good nor really useful, so let's remove it.

release/scripts/templates_osl/westin_closure.osl

@@ -1,12 +0,0 @@
-
-shader node_westin_bsdf(
-	color Color = 0.8,
-	float Roughness = 0.5,
-	float Edginess = 0.2,
-	normal Normal = N,
-	output closure color Sheen = 0,
-	output closure color Backscatter = 0)
-{
-	Sheen = Color * westin_sheen(Normal, Roughness);
-	Backscatter = Color * westin_backscatter(Normal, Edginess);
-}