PR: 1794
Submitted by: Peter Sylvester <peter.sylvester@edelweb.fr>
Reviewed by: steve

Remove unnecessary code for srp and to add some comments to
s_client.

- the callback to provide a user during client connect is
no longer necessary since rfc 5054 a connection attempt
with an srp cipher and no user is terminated when the
cipher is acceptable

- comments to indicate in s_client the (non-)usefulness of
th primalaty tests for non known group parameters.