Revert to the old TLS API, but keep certs as mg_str for DER

src/net_builtin.c

@@ -544,7 +544,6 @@ static struct mg_connection *accept_conn(struct mg_connection *lsn,
   c->fn_data = lsn->fn_data;
   mg_call(c, MG_EV_OPEN, NULL);
   mg_call(c, MG_EV_ACCEPT, NULL);
-  if (lsn->is_tls) mg_tls_init(c, mg_str(""));
   return c;
 }