vo_sixel: change exit-clear handling to OPT_REPLACED

Easier to keep track of when we do want to remove it.

video/out/vo_sixel.c

@@ -618,10 +618,9 @@ const struct vo_driver video_out_sixel = {
         {"rows", OPT_INT(opts.rows)},
         {"cols", OPT_INT(opts.cols)},
         {"config-clear", OPT_BOOL(opts.config_clear), },
-        {"exit-clear", OPT_BOOL(opts.alt_screen),
-            .deprecation_message = "replaced by --vo-sixel-alt-screen"},
         {"alt-screen", OPT_BOOL(opts.alt_screen), },
         {"buffered", OPT_BOOL(opts.buffered), },
+        {"exit-clear", OPT_REPLACED("vo-sixel-alt-screen")},
         {0}
     },
     .options_prefix = "vo-sixel",