Remove attempt to override TLS 1.3 server ciphersuites

Remove attempt to override TLS 1.3 server ciphersuites

This was unnecessary _and_ broken!

It was unnecessary because the default list of TLS 1.3 ciphersuites
has always been pretty reasonable.

It was broken because:
 - SSL_CTX_set_cipher_list only affects the list of TLS 1.2 ciphersuites.
 - There have _never_ been a set of macros  named TLS1_3_TXT_*
   in any openssl version, as far as I can tell.