Add OPENSSL_cleanup to tls_shutdown function

This prevents a direct leak in OPENSSL_init_crypto (called from
OPENSSL_init_ssl).

Add shim version of OPENSSL_cleanup because it is missing in LibreSSL on
OpenBSD.
67 jobs for !5593 with matthijs-fix-openssl-init-ssl-leak in 18 minutes and 21 seconds (queued for 12 seconds)
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