Apple removed CGColorConverter even if it was publicly exposed in iOS 9.3,
not that I recall any API that consumed it...
It was replaced by a new, very close, type named CGColorConversionInfo and
the existing code and tests were updated to the new API.
So for `CGColorConverter` we're
* iOS: Obsoleted + code removal
* tvOS: Obsoleted + code removal
* watchOS: the API can be removed as it was not exposed in a stable release
* macOS: it was not enabled (did not work)
* [tests] Adjust ApiCMAttachmentTest so it knows how to create the new CGColorConversionInfo type
Sebastien Pouliot