[Book 3] Listing 44 to Listing 46, the `scatter()` method in class diffuse_light may need to be marked as removed

[InchChou]

In book 2 chapter 7.1 we introduce class diffuse_light and implement method scatter().

Book 3 Listing 44 change the signature of scatter() of parent class material, so all the derived class should also be changed. But we can't find diffuse_light's scatter() method that modified in book 3.

So the scatter() method in class diffuse_light may need to be marked as removed or changed the signature to match the material::scatter()'s signature.

[hollasch]

Done.