cgal: update from 3.9 to 4.3 (really)

The previous version bump didn't actually do anything; it changed the
version/url but didn't change the hash. For some reason the (new) URL
returned the same old package with the same old hash (or so it seems).

This time the package is really updated, as can be seen from the version
number in $cgal/include/CGAL/version.h.

This change unbreaks openscad.
cgal: expression cleanup