remove unused imports.
remove empty AApplyExpressionTraceCoreDefinitionAssistantInterpreter.
remove empty assistant AAssignmentDefinitionAssistantInterpreter
remove empty assistant ABracketedExpressionTraceCoreDefinitionAssitantInterpreter
remove assistant AClassInvariantDefinitionAssistantInterpreter
AConcurrentExpressionTraceCoreDefinitionAssistantInterpreter removed.