Stop supporting Homebrew in robotology-superbuild Continuous Integration and direct macOS users to conda?

[traversaro]

Hi everyone! In robotology-superbuild repo there is an issue that could be interesting for the community, especially that part of the community that uses macOS: robotology/robotology-superbuild#842 . The discussion is happening there, but this discussion is to make every macOS user that watches robotology/community aware of this discussion.

cc @robotology/everyone