d3d [2]: Optional callback infrastructure for implicit texture surface destruction.

[Markus Amsler]

H. Verbeet wrote:
> I think the callback should be non-optional.

I think you're right. I wanted to avoid code duplication for default 
callbacks in ddraw, d3d8, d3d9, wined3d. But the non-optional way would 
avoid duplication in wined3d, and it's more elegant => non-optional wins 
with 1:2. I will rework them.