patch 8.2.4677: the Athena GUI support is outdated

Problem:    The Athena GUI support is outdated.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/gui_init.vim b/src/testdir/gui_init.vim
index 42b2bca..4fa6cbc 100644
--- a/src/testdir/gui_init.vim
+++ b/src/testdir/gui_init.vim
@@ -1,6 +1,6 @@
 " gvimrc for test_gui_init.vim
 
-if has('gui_athena') || has('gui_motif') || has('gui_gtk2') || has('gui_gtk3')
+if has('gui_motif') || has('gui_gtk2') || has('gui_gtk3')
   set guiheadroom=0
   set guioptions+=p
 endif