curl_multi_cleanup(3) on macOS

The text 45a1889d2d33, as Mac OS X 10.8.5, Mac OS X 10.8.4, Mac OS X 10.8.3, Mac OS X 10.8.2, Mac OS X 10.8.1, Mac OS X 10.8 shipped it.

close down a multi session

curl_multi_cleanup(3) on macOS now