patch 8.0.1135: W_WINCOL() is always the same

Problem:    W_WINCOL() is always the same.
Solution:   Expand the macro.
diff --git a/src/structs.h b/src/structs.h
index 94d7391..768ff58 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2700,8 +2700,7 @@
     int		w_height;	    /* number of rows in window, excluding
 				       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.
-				       use W_WINCOL() */
+    int		w_wincol;	    /* Leftmost column of window in screen. */
     int		w_width;	    /* Width of window, excluding separation.
 				       use W_WIDTH() */
     int		w_vsep_width;	    /* Number of separator columns (0 or 1).