Cycles: Remove the experimental CUDA kernel.

This commit removes the experimental CUDA kernel, making SSS and CMJ
regular features.

Several improvements have been made in the past few
weeks (thanks Sergey!) which make SSS render several times faster (2-3x
compared to 2.76b) on the GPU, and the increased VRAM usage has also been
fixed. Therefore the experimental kernel is no longer needed.

Differential Revision: https://developer.blender.org/D1726

Manual has been updated: too:
https://www.blender.org/manual/render/cycles/features.html

source/blender/editors/space_node/drawnode.c

@@ -1057,19 +1057,6 @@ static void node_shader_buts_anisotropic(uiLayout *layout, bContext *UNUSED(C),
 
 static void node_shader_buts_subsurface(uiLayout *layout, bContext *C, PointerRNA *ptr)
 {
-	/* SSS only enabled in Experimental Kernel */
-	PointerRNA scene = CTX_data_pointer_get(C, "scene");
-	if (scene.data) {
-		PointerRNA cscene = RNA_pointer_get(&scene, "cycles");
-		if (cscene.data &&
-		    ((U.compute_device_type != USER_COMPUTE_DEVICE_NONE) &&
-		     (RNA_enum_get(&cscene, "device") == 1) &&
-		     (RNA_enum_get(&cscene, "feature_set") == 0)))
-		{
-			uiItemL(layout, IFACE_("Only enabled in experimental GPU kernel"), ICON_ERROR);
-		}
-	}
-
 	uiItemR(layout, ptr, "falloff", 0, "", ICON_NONE);
 }