merge-one-file: use rmdir -p

The flag is universally available, even on VMS; use it.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-merge-one-file.sh

@@ -26,11 +26,7 @@ case "${1:-.}${2:-.}${3:-.}" in
 	fi
 	if test -f "$4"; then
 		rm -f -- "$4" &&
-		dn="$4" &&
-		while dn=$(expr "$dn" : '\(.*\)/') && rmdir "$dn" 2>/dev/null
-		do
-			:;
-		done
+		rmdir -p "$(expr "$4" : '\(.*\)/')" 2>/dev/null
 	fi &&
 		exec git-update-index --remove -- "$4"
 	;;