patch 8.2.4677: the Athena GUI support is outdated

Problem:    The Athena GUI support is outdated.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_clientserver.vim b/src/testdir/test_clientserver.vim
index 03d201d..aebbc2f 100644
--- a/src/testdir/test_clientserver.vim
+++ b/src/testdir/test_clientserver.vim
@@ -63,8 +63,8 @@
     " the GUI and check that the remote command still works.
     " Need to wait for the GUI to start up, otherwise the send hangs in trying
     " to send to the terminal window.
-    if has('gui_athena') || has('gui_motif')
-      " For those GUIs, ignore the 'failed to create input context' error.
+    if has('gui_motif')
+      " For this GUI ignore the 'failed to create input context' error.
       call remote_send(name, ":call test_ignore_error('E285') | gui -f\<CR>")
     else
       call remote_send(name, ":gui -f\<CR>")