Port and simplify example sh script

* doc/misc/org.texi (noweb-ref): Simplify shell script example and
don’t use ‘tail -1’, which is not portable.

doc/misc/org.texi

@@ -15327,14 +15327,9 @@ inheritance}).}.
    |sed '1d' \
  #+END_SRC
 
- ** sort by the percent full
+ ** output mount point of fullest disk
  #+BEGIN_SRC sh
-   |awk '@{print $5 " " $6@}'|sort -n |tail -1 \
- #+END_SRC
-
- ** extract the mount point
- #+BEGIN_SRC sh
-   |awk '@{print $2@}'
+   |awk '@{if (u < +$5) @{u = +$5; m = $6@}@} END @{print m@}'
  #+END_SRC
 @end example