Revert logging a warning when authenticator is configured but server does not challenge

introduced a log message when a server does not respond with an authentication challenge but the client is configured with auth:

localhost/127.0.0.1:9042 did not send an authentication challenge; This is suspicious because the driver expects authentication (configured auth provider = ...)

After some discussion we've identified some use cases where this could be valid.

Instead we should have a mechanism for the user to communicate whether or not authentication should be required, and warn and/or fail in this case. Until such a feature is implemented we should remove this warning.