science/massxpert: Improve port

• Remove unneeded dependency on libpcre. [1]
• Add USES= compiler:c++17-lang, consistent with set(CMAKE_CXX_STANDARD 17) (line 65 of CMakeLists.txt). [1]
• Remove USES= tar:bzip2. [1]
• Set WWW in pkg-descr to the site reported by README.md.

Reported by: diizzy [1]
Reviewed by: diizzy
Approved by: gerald (mentor)
Differential Revision: https://reviews.freebsd.org/D35138