We might want to open an RFC for fragment refs which could solve the one
remaining use case in a better way but at least let us get the deprecation
in.
The "Browser Support" section of react-dom indicates that IE9 and above
is supported, but fails to note that the support does require additional
polyfills in some cases. A link is added to the javascript environment
docs which already explains the polyfills required (Map, Set and rAF).
