SSL_CTX_free() decrements the reference count of ctx, and removes the
SSL_CTX object pointed to by ctx and frees up the allocated memory if the
the reference count has reached 0.
It also calls the free()ing procedures for indirectly affected items, if
applicable: the session cache, the list of ciphers, the list of Client CAs,
the certificates and keys.
WARNINGS
If a session-remove callback is set (SSL_CTX_sess_set_remove_cb()), this
callback will be called for each session being freed from ctx's
session cache. This implies, that all corresponding sessions from an
external session cache are removed as well. If this is not desired, the user
should explicitly unset the callback by calling
SSL_CTX_sess_set_remove_cb(ctx, NULL) prior to calling SSL_CTX_free().
RETURN VALUES
SSL_CTX_free() does not provide diagnostic information.
