This removes package tangling between authentication and authentication.ldap
The Registry interface was around to limit the methods available when using registerAuthentication, but the methods available cause no more confusion that the configure(HttpConfiguration) methods. The additional complexity of maintaining the interfaces was not worth the minor benefits.
This is necessary to avoid exporting null AuthenticationManager and null UserDetailsService in some instances. It also allows the removal of code that looks up a bean but excludes the look up of the bean by a particular name.