From mingw-w64.

This is arbitrary, we don't do it for any of the other resource bindings
either, and the wined3d_state structure is assumed to be zero-initialized.

This used to work out in practice because swapchain surfaces were always
considered render targets, but that's no longer true. We can just remove the
check, because surface_blt_special() already contains a proper check itself
anyway.

These use the generic GL_DEPTH_COMPONENT internal format, and can't be used
for texturing.