Bug#883440: gnome: Don't require gtk2

[Jeremy Bicha]

Package: gnome
Version: 1:3.22+6
Tags: buster

I think it would be a nice goal if Debian GNOME didn't install gtk2 by
default for the Buster release. Therefore, I'm opening this tracker
bug so we can easily see how close we are to achieving that goal.

The GTK developers declared gtk3 as stable with its 3.22 release in
September 2016.

The corresponding Ubuntu tracker bug is https://launchpad.net/bugs/1585903

Thanks,
Jeremy Bicha