apps/s_socket.c: Fix do_accept

do_accept() checked that the peer IP address had a PTR record, and would
fail if not.  The retrieved named was then never used, even though passed
around.  All this is unnecessary, so we remove it.

Fixes #3407

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6018)