Elide OPENSSL_INIT_set_config_filename() for no-stdio build

Strictly speaking, it isn't stdio and file access which offend me here;
it's the fact that UEFI doesn't provide a strdup() function. But the
fact that it's pointless without file access is a good enough excuse for
compiling it out.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>