crypto: fix error in deprecation message

The deprecation message for `crypto.Credentials` says to use
`tls.createSecureContext` but the correct property to use is
`tls.SecureContext()`.

Fix the deprecation message and add a test that checks the mappings of
deprecated properties and their warning messages.

PR-URL: https://github.com/nodejs/node/pull/6344


Reviewed-By: James M Snell <jasnell@gmail.com>