science/massxpert: Improve port
- Remove unneeded dependency on libpcre.
- Add compiler:c++17-lang - Add USES= compiler:c++17-lang, consistently with
set(CMAKE_CXX_STANDARD 17) (line 65 of CMakeLists.txt).
- Remove USES= tar:bzip2.
- Set WWW in pkg-descr to the site reported by README.md.
Reported by: diizzy