apps/openssl.c: avoid memory leaks

The trace API doesn't know that the BIOs we give it, let alone those
we attach to callbacks as 'void *data', need to be cleaned up.  This
must be done in the application.

To ensure this cleanup is done as late as possible, use atexit().

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8198)