patch 8.0.1136: W_WIDTH() is always the same

Problem:    W_WIDTH() is always the same.
Solution:   Expand the macro.
diff --git a/src/structs.h b/src/structs.h
index 768ff58..4582dca 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2701,8 +2701,7 @@
 				       status/command/winbar line(s) */
     int		w_status_height;    /* number of status lines (0 or 1) */
     int		w_wincol;	    /* Leftmost column of window in screen. */
-    int		w_width;	    /* Width of window, excluding separation.
-				       use W_WIDTH() */
+    int		w_width;	    /* Width of window, excluding separation. */
     int		w_vsep_width;	    /* Number of separator columns (0 or 1).
 				       use W_VSEP_WIDTH() */
     /*