Remove unused Scope argument from artifact name related APIs.
Additionally, this reverts terminology back to calling these "artifact names", and not "artifact refs", which is a terminology which crept in from various underlying implementations.
Summary of changes:
* _artifact.py:
- get_dependency_refs() renamed to get_dependency_artifact_names()
- get_dependency_artifact_names() loses the Scope argument
- Consequently, a huge and needless XXX comment is removed
* _artifactelement.py:
- _new_from_artifact_ref() renamed to _new_from_artifact_name()
- get_dependency_refs() renamed to get_dependency_artifact_names()
- get_dependency_artifact_names() loses the Scope argument
* _project.py:
- Now call _new_from_artifact_name()
- Removes a legacy XXX comment which is not particularly relevant
* element.py:
- __get_dependency_refs() renamed to __get_dependency_artifact_names()
- Adapt __get_last_build_artifact() to updated API names.