code: def DeregisterDefinition(self, artifact_definition):
      
      artifact_definition_name = artifact_definition.name.lower()
      if artifact_definition_name not in self._artifact_definitions:
        raise KeyError(
            'Artifact definition not set for name: {0:s}.'.format(
                artifact_definition.name))
  
      del self._artifact_definitions[artifact_definition_name]
docs: Deregisters an artifact definition.
  
      Artifact definitions are identified based on their lower case name.
  
      Args:
        artifact_definition (ArtifactDefinition): an artifact definition.
  
      Raises:
        KeyError: if an artifact definition is not set for the corresponding name.