adduser-old.c: Remove program

adduser-old.c: Remove program

This program has 10 calls to gets(3) according to grep(1).  That
makes it a very unsafe program which should not be used at all.
Let's kill the program already.

See what gets(3) has to say:

SYNOPSIS
       #include <stdio.h>

       [[deprecated]] char *gets(char *s);

DESCRIPTION
       Never use this function.

       ...

BUGS
       Never use gets().  Because it is impossible to tell with‐
       out knowing the  data  in  advance  how  many  characters
       gets()  will  read,  and  because gets() will continue to
       store characters past the end of the buffer,  it  is  ex‐
       tremely dangerous to use.  It has been used to break com‐
       puter security.  Use fgets() instead.

       For more information, see CWE‐242 (aka "Use of Inherently
       Dangerous Function") at http://cwe.mitre.org/data/defini‐
       tions/242.html

Acked-by: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>