patch 8.2.4677: the Athena GUI support is outdated

Problem:    The Athena GUI support is outdated.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/gui.c b/src/gui.c
index 3b8c0d0..68ac9d8 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -53,15 +53,6 @@
 static int disable_flush = 0;	// If > 0, gui_mch_flush() is disabled.
 
 /*
- * The Athena scrollbars can move the thumb to after the end of the scrollbar,
- * this makes the thumb indicate the part of the text that is shown.  Motif
- * can't do this.
- */
-#if defined(FEAT_GUI_ATHENA)
-# define SCROLL_PAST_END
-#endif
-
-/*
  * gui_start -- Called when user wants to start the GUI.
  *
  * Careful: This function can be called recursively when there is a ":gui"
@@ -445,8 +436,7 @@
     gui.menu_width = 0;
 # endif
 #endif
-#if defined(FEAT_TOOLBAR) && (defined(FEAT_GUI_MOTIF) || defined(FEAT_GUI_ATHENA) \
-	|| defined(FEAT_GUI_HAIKU))
+#if defined(FEAT_TOOLBAR) && (defined(FEAT_GUI_MOTIF) || defined(FEAT_GUI_HAIKU))
     gui.toolbar_height = 0;
 #endif
 #if defined(FEAT_FOOTER) && defined(FEAT_GUI_MOTIF)
@@ -789,7 +779,7 @@
 	balloonEval = gui_mch_create_beval_area(gui.drawarea, NULL,
 						     &general_beval_cb, NULL);
 # else
-#  if defined(FEAT_GUI_MOTIF) || defined(FEAT_GUI_ATHENA)
+#  if defined(FEAT_GUI_MOTIF)
 	{
 	    extern Widget	textArea;
 	    balloonEval = gui_mch_create_beval_area(textArea, NULL,
@@ -1441,11 +1431,11 @@
 	text_area_y += gui.tabline_height;
 #endif
 
-#if defined(FEAT_TOOLBAR) && (defined(FEAT_GUI_MOTIF) || defined(FEAT_GUI_ATHENA) \
+#if defined(FEAT_TOOLBAR) && (defined(FEAT_GUI_MOTIF) \
 	|| defined(FEAT_GUI_HAIKU) || defined(FEAT_GUI_MSWIN))
     if (vim_strchr(p_go, GO_TOOLBAR) != NULL)
     {
-# if defined(FEAT_GUI_ATHENA) || defined(FEAT_GUI_HAIKU)
+# if defined(FEAT_GUI_HAIKU)
 	gui_mch_set_toolbar_pos(0, text_area_y,
 				gui.menu_width, gui.toolbar_height);
 # endif
@@ -2043,10 +2033,10 @@
     old_curwin = curwin;
 
     /*
-     * We need to make sure this is cleared since Athena doesn't tell us when
-     * he is done dragging.  Do the same for GTK.
+     * We need to make sure this is cleared since GTK doesn't tell us when
+     * the user is done dragging.
      */
-#if defined(FEAT_GUI_ATHENA) || defined(FEAT_GUI_GTK)
+#if defined(FEAT_GUI_GTK)
     gui.dragged_sb = SBAR_NONE;
 #endif
 
@@ -3410,10 +3400,10 @@
     prev_col = col;
 
     /*
-     * We need to make sure this is cleared since Athena doesn't tell us when
-     * he is done dragging.  Neither does GTK+ 2 -- at least for now.
+     * We need to make sure this is cleared since GTK doesn't tell us when
+     * the user is done dragging.
      */
-#if defined(FEAT_GUI_ATHENA) || defined(FEAT_GUI_GTK)
+#if defined(FEAT_GUI_GTK)
     gui.dragged_sb = SBAR_NONE;
 #endif
 }
@@ -3952,9 +3942,6 @@
     sb->wp = wp;
     sb->type = type;
     sb->value = 0;
-#ifdef FEAT_GUI_ATHENA
-    sb->pixval = 0;
-#endif
     sb->size = 1;
     sb->max = 1;
     sb->top = 0;
@@ -4336,7 +4323,7 @@
 		y += gui.menu_height;
 #endif
 
-#if defined(FEAT_TOOLBAR) && (defined(FEAT_GUI_MSWIN) || defined(FEAT_GUI_ATHENA) \
+#if defined(FEAT_TOOLBAR) && (defined(FEAT_GUI_MSWIN) \
 	|| defined(FEAT_GUI_HAIKU))
 	    if (vim_strchr(p_go, GO_TOOLBAR) != NULL)
 		y += gui.toolbar_height;
@@ -4369,25 +4356,10 @@
 	    }
 	}
 
-	// Reduce the number of calls to gui_mch_set_scrollbar_thumb() by
-	// checking if the thumb moved at least a pixel.  Only do this for
-	// Athena, most other GUIs require the update anyway to make the
-	// arrows work.
-#ifdef FEAT_GUI_ATHENA
-	if (max == 0)
-	    y = 0;
-	else
-	    y = (val * (sb->height + 2) * gui.char_height + max / 2) / max;
-	if (force || sb->pixval != y || sb->size != size || sb->max != max)
-#else
 	if (force || sb->value != val || sb->size != size || sb->max != max)
-#endif
 	{
 	    // Thumb of scrollbar has moved
 	    sb->value = val;
-#ifdef FEAT_GUI_ATHENA
-	    sb->pixval = y;
-#endif
 	    sb->size = size;
 	    sb->max = max;
 	    if (gui.which_scrollbars[SBAR_LEFT]
@@ -5122,7 +5094,7 @@
 	    || defined(FEAT_GUI_HAIKU)) \
 	    && defined(FEAT_TOOLBAR)) || defined(PROTO)
 /*
- * This is shared between Athena, Haiku, Motif, and GTK.
+ * This is shared between Haiku, Motif, and GTK.
  */
 
 /*