openssl: Fix compilation with OPENSSL_API_COMPAT=0x10100000L

With OPENSSL_API_COMPAT=0x10100000L (OpenSSL 1.1 API), the cleanup
functions are unavailable (they're no-ops anyway in OpenSSL 1.1). The
replacements for SSL_load_error_strings, SSLeay_add_ssl_algorithms, and
OpenSSL_add_all_algorithms are called automatically [1][2]. SSLeay() is
now called OpenSSL_version_num().

[1]: https://www.openssl.org/docs/man1.1.0/ssl/OPENSSL_init_ssl.html
[2]: https://www.openssl.org/docs/man1.1.0/crypto/OPENSSL_init_crypto.html

Closes #992