Revisiting system packages

[springmeyer]

Per chat with @kkaefer - Mason system packages are no longer in common use. We should consider fixing the problems we've experienced in using them. And if this is not viable or desirable we should move on deprecating and removing them.

The are not in common use because of the relative ease, for example, of just doing -lz instead of trying to get zlib system working on multiple architectures.

Another problem with system packages is that they are not published, which makes their usage inconsistent and not viable currently from mason.cmake. Originally there was no need to publish them because they were empty anyway and all of the logic was in the script.sh. That’s no longer true now that we are using mason.ini.

• previously: #65