patch 8.2.4677: the Athena GUI support is outdated

Problem:    The Athena GUI support is outdated.
Solution:   Remove the Athena GUI code.
diff --git a/src/testdir/test_highlight.vim b/src/testdir/test_highlight.vim
index 4b8cd86..51a2524 100644
--- a/src/testdir/test_highlight.vim
+++ b/src/testdir/test_highlight.vim
@@ -759,7 +759,7 @@
   elseif has('gui_gtk2') || has('gui_gnome') || has('gui_gtk3')
     " expect is DEFAULT_FONT of gui_gtk_x11.c
     call assert_match('hi Normal\s*font=Monospace 10', hlNormal)
-  elseif has('gui_motif') || has('gui_athena')
+  elseif has('gui_motif')
     " expect is DEFAULT_FONT of gui_x11.c
     call assert_match('hi Normal\s*font=7x13', hlNormal)
   elseif has('win32')