DOCSP-51018: remove libressl (#128)

(cherry picked from commit 44a8719)

Author: rustagir

source/connect/tls.txt

@@ -151,7 +151,6 @@ by the cmake flag ``ENABLE_SSL``, which is set to ``AUTO`` by default. This flag
 
 - ``AUTO``: Links to the system's native TLS library, or attempts to find OpenSSL. This is the default value.
 - ``OPENSSL``: Links to OpenSSL (libssl). An optional install path may be specified with ``OPENSSL_ROOT``.
-- ``LIBRESSL`` (Deprecated): Links to LibreSSL's libtls. You can link to LibreSSL's compatible libssl by setting ``OPENSSL``.
 - ``WINDOWS``: Links to Secure Channel, the native TLS library on Windows.
 - ``DARWIN``: Links to Secure Transport, the native TLS library on macOS.
 - ``OFF``: Disables TLS support.
@@ -182,26 +181,6 @@ The Online Certificate Status Protocol (OCSP) is fully supported
 when using OpenSSL 1.0.1+. However, when a ``crl_file`` is set with `mongoc_ssl_opt_t <{+api-libmongoc+}/mongoc_ssl_opt_t.html>`__ and the ``crl_file`` revokes
 the server's certificate, the certificate is considered revoked, even if the certificate has a valid stapled OCSP response.
 
-.. tip::
- 
-   For more information about OCSP, see `RFC 6960 <https://tools.ietf.org/html/rfc6960>`__.
-
-LibreSSL / libtls (Deprecated)
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The MongoDB C Driver supports LibreSSL through the use of OpenSSL compatibility checks when configured to compile against
-``openssl``. It also supports the new ``libtls`` library when configured to build against ``libressl``.
-
-When compiled with LibreSSL, the ``crl_file`` option of a `mongoc_ssl_opt_t <{+api-libmongoc+}/mongoc_ssl_opt_t.html>`__ is not supported,
-and will issue an error if used. Setting ``tlsDisableOCSPEndpointCheck`` and ``tlsDisableCertificateRevocationCheck`` has no effect.
-
-The Online Certificate Status Protocol (OCSP) is partially supported
-with the following notes:
-
-- Must-Staple extension (see `RFC 7633 <https://tools.ietf.org/html/rfc7633>`__) is ignored
-- Connection will continue if a Must-Staple certificate is presented without a stapled response and the OCSP responder is down
-- Connection will not continue if the client receives a revoked response from an OCSP responder
-
 .. tip::
 
    For more information about OCSP, see `RFC 6960 <https://tools.ietf.org/html/rfc6960>`__.