[RFC] Simplified Homebrew formula

Removed unnecessary cmake modifications, and manual building of
dependencies. Updates to Makefile remove the need.
> So we should leave the wiki as it is to avoid confusion. Is this something that may also be a problem for homebrew users (is there a risk that homebrew will re-use a cached cmake config)?

That's a good question.  Unfortunately, I'm not sure.  I use Homebrew, but I haven't made any formula.  I would have assumed Homebrew would do a clean build, but perhaps not.  If it doesn't, then yes, I think you're right: running cmake explicity is best.