At this point it doesn't really add anything anymore.

The idea is to make it clear that wined3d_texture_load is responsible
for checking the color key for changes. Once we can do color keying in
the shader we also have one place where we can disable the surface
conversion.

This fixes a regression with color keyed mipmaps that was introduced by
ee8a5b7d. surface_load for level n+1
would call texture_force_reload, thus removing level n from the GL
texture.