emoji dns-prefetch not part of wp_resource_hints

This is a two part issue and solution:

1. Recently, WordPress removed dns-prefetch for emoji. So it’s no longer part of wp_resource_hints. So disable_emojis_remove_dns_prefetch() function can be removed.
2. For older versions, all you need to disable dns-prefetch replace
   add_filter( 'wp_resource_hints', 'disable_emojis_remove_dns_prefetch', 10, 2 ); with a dedicated filter that was added in v4.6:
   add_filter( 'emoji_svg_url', '__return_false');

The second part also helps make your plugin compatible with ClassicPress, since ClassicPress doesn’t use https://s.w.org/images/core/emoji/

I’d submit a PR if there was a repo. Here’s an example fixed in Autoptimize.