Roll back FontAwesome 5 changes.

I'm more and more convinced that eliminating the FontAwesome 5 upgrade is the best choice, not all donuts succeed with the hole. It's more the downside than the upside. I say this after carefully looking at prosilver and all our extensions that make extensive use of icons, it is simply shameful how the authors of FA have handled this change.

Complains can be seen at: https://area51.phpbb.com/phpBB/viewtopic.php?f=81&t=75446

And I am sure more will come once released there at phpbb DOT com.