Don't set the _file member of the FILE when opening a FTP connection.

Nothing in libftpio uses _file, and the only consumer in the tree
(sysinstall) doesn't invoke fileno() on the FILE.

MFC after:	2 months

lib/libftpio/ftpio.c

@@ -292,7 +292,6 @@ ftpLoginAf(char *host, int af, char *user, char *passwd, int port, int verbose,
     fp = NULL;
     if (n && ftp_login_session(n, host, af, user, passwd, port, verbose) == SUCCESS) {
 	fp = funopen(n, ftp_read_method, ftp_write_method, NULL, ftp_close_method);	/* BSD 4.4 function! */
-	fp->_file = n->fd_ctrl;
     }
     if (retcode) {
 	if (!n)