science/massxpert: Improve port
- Remove unneeded dependency on libpcre. - 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