Remove `core_graphics::private::CGSRegion`
This is a private API on macOS. This code was added for use in servo-glutin and was not used outside of that as far as I know (by doing various code searches).
Fixes #656.
If there is someone using this, they can take the code that used to be here and use it within their own codebase rather than us maintaining it.
Perhaps we can do a quick turnaround here and release the 0.11 series in order to not block the pending PRs that should be merged?
I want to go through more of the backlog of things to make sure that we're not missing things. There's at least a couple that should land! Taking a couple of days for that seems fine...
Propagating all of this stuff into the broader ecosystem is going to be some serious work.