Xcode proj fix

this is a fix attempt for https://github.com/openframeworks/openFrameworks/issues/2931
note that this is against master, there's some changes already to ofUtils, etc.... 

I'm not so familiar with the openFrameworks coding style, but generally I find keeping dead code around to be a nuisance and a distraction. The code is perfectly available in the revision history. A note saying `// Note that we don't make project.xcworkspace; see issue #2931` will be sufficient documentation.