bsdinstall/distfetch: Fix double include

[asiciliano]

Summary

#include <sys/param.h>

#include <bsddialog.h>
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <stdio.h> <----------- GOOD (before fetch.h)
#include <fetch.h>
#include <stdio.h> <------------ BAD, double
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

Test Plan

Trivial