patch 8.2.4677: the Athena GUI support is outdated

Problem:    The Athena GUI support is outdated.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/runtime/doc/gui.txt b/runtime/doc/gui.txt
index 84d6984..df812c9 100644
--- a/runtime/doc/gui.txt
+++ b/runtime/doc/gui.txt
@@ -25,7 +25,7 @@
 
 First you must make sure you actually have a version of Vim with the GUI code
 included.  You can check this with the ":version" command, it says "with xxx
-GUI", where "xxx" is X11-Motif, X11-Athena, Photon, GTK2, GTK3, etc., or
+GUI", where "xxx" is X11-Motif, Photon, GTK2, GTK3, etc., or
 "MS-Windows 32 bit GUI version".
 
 How to start the GUI depends on the system used.  Mostly you can run the
@@ -108,7 +108,7 @@
 Vim.  These are 'guicursor', 'guifont', 'guipty' and 'guioptions'.  They are
 documented in |options.txt| with all the other options.
 
-If using the Motif or Athena version of the GUI (but not for the GTK+ or
+If using the Motif version of the GUI (but not for the GTK+ or
 Win32 version), a number of X resources are available.  See |gui-resources|.
 
 Another way to set the colors for different occasions is with highlight
@@ -236,7 +236,7 @@
 include the 'h' flag in 'guioptions'.  Then the scrolling is limited by the
 text of the current cursor line.
 
-							*athena-intellimouse*
+							*motif-intellimouse*
 If you have an Intellimouse and an X server that supports using the wheel,
 then you can use the wheel to scroll the text up and down in gvim.  This works
 with XFree86 4.0 and later, and with some older versions when you add patches.
@@ -746,7 +746,7 @@
 simple.
 
 							*gui-toolbar*
-The toolbar is currently available in the Win32, Athena, Motif, GTK+ (X11),
+The toolbar is currently available in the Win32, Motif, GTK+ (X11),
 and Photon GUI.  It should turn up in other GUIs in due course.  The
 default toolbar is setup in menu.vim.
 The display of the toolbar is controlled by the 'guioptions' letter 'T'.  You
@@ -862,7 +862,7 @@
 When splitting the window the window toolbar is not copied to the new window.
 
 							*popup-menu*
-In the Win32, GTK+, Motif, Athena and Photon GUI, you can define the
+In the Win32, GTK+, Motif and Photon GUI, you can define the
 special menu "PopUp".  This is the menu that is displayed when the right mouse
 button is pressed, if 'mousemodel' is set to popup or popup_setpos.
 Example: >