Remove `SHADOW_ATTENUATION` spatial light shader built-in

tutorials/shaders/shader_reference/spatial_shader.rst

@@ -405,8 +405,6 @@ If you want the lights to add together, add the light contribution to ``DIFFUSE_
 +-----------------------------------+----------------------------------------------------+
 | in float **ATTENUATION**          | Attenuation based on distance or shadow.           |
 +-----------------------------------+----------------------------------------------------+
-| in vec3 **SHADOW_ATTENUATION**    |                                                    |
-+-----------------------------------+----------------------------------------------------+
 | in vec3 **ALBEDO**                | Base albedo.                                       |
 +-----------------------------------+----------------------------------------------------+
 | in vec3 **BACKLIGHT**             |                                                    |