Implementation support for AWT/Swing using GTK2 on Linux is now deprecated for removal.

With the announcement of the GTK4 release in December 2020, the GTK 2 toolkit is reaching its end of life. GTK2 support is therefore expected to be removed some time after no JDK supported platform needs it.

GTK3 is the current default and Swing applications which opt-in to using GTK2 on Linux by setting the System Property `-Djdk.gtk.version=2` will now see the following warning printed:

`WARNING: the GTK 2 library is deprecated and its support will be removed in a future release`.