Prevent registration related entities from being hosts

Problem/Motivation

Currently the registration host entity handler throws a deprecation message if it detects that the attempted host is a registration entity. This should instead generate an exception, and the settings entity type should also be checked, since it too should never be a host entity.

Steps to reproduce

Call RegistrationHostEntityHandler::createHostEntity with a registration entity.

Proposed resolution

Throw an InvalidArgumentException

Remaining tasks

Throw the exceptions and add a test.

User interface changes

None

API changes

As noted above.

Data model changes

None