Remove null check, per review feedback.  Note this in the docs.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1135)
diff --git a/doc/ssl/SSL_SESSION_get_protocol_version.pod b/doc/ssl/SSL_SESSION_get_protocol_version.pod
index bc6f25c..a033fdd 100644
--- a/doc/ssl/SSL_SESSION_get_protocol_version.pod
+++ b/doc/ssl/SSL_SESSION_get_protocol_version.pod
@@ -21,7 +21,8 @@
 version used for the session; this number matches the constants I<e.g.>
 B<TLS1_VERSION> or B<TLS1_2_VERSION>.
 
-If the function is passed the NULL pointer for the session B<s>, 0 is returned.
+Note that the SSL_SESSION_get_protocol_version() function
+does B<not> perform a null check on the provided session B<s> pointer.
 
 =head1 SEE ALSO