Mac OS X Backend: Removing clip that is no longer needed

[mdehoon]

Same thing as for the Cairo backend (pull request #1538). The same simplifications can be made in the Mac OS X backend.

[mdboom]

@mdehoon: Do you think this may have something to do with #1563?

[mdehoon]

No that is a separate issue.

[dmcdougall]

Thanks @mdehoon. Do we have tests for the OS X infrastructure? If not, it'd be nice if, as a larger more ambitious goal, the C/C++/Objc code got code coverage. Though, having said that, this might be a moot point if we decide to make the move towards a Cython-backed infrastructure.

[mdehoon]

No we don't have specific tests for the Mac OS X backend. Realistically speaking I don't think I will find time to write such tests, but I wouldn't object if somebody else does.
Even if we do go towards a Cython-backed infrastructure, I think it would be a really bad idea to convert the Mac OS X backend to Cython. For one thing, it's hard to have the event loop, ObjC memory management, and Python reference counting play nice with each other. I don't want to add Cython to the mix. Also, let's not fix what is not broken.