Remove unportable test

Remove unportable test

The ssl test "IPv4 host with CIDR mask does not match" apparently has
a portability problem.  Some operating systems don't reject the host
name specification "192.0.2.1/32" as an IP address, and that is then
later rejected when the SNI is set, which results in a different error
message that the test is supposed to verify.

The value of the test has been questioned in the discussion, and it
was suggested that removing it would be an acceptable fix, so that's
what this is doing.

Reported-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Bug: #17522
Discussion: https://www.postgresql.org/message-id/flat/17522-bfcd5c603b5f4daa%40postgresql.org