reproducible with 070218_1

Appears as part of Issue 80953 fix, 
It's not necessary but is good to be more clear user don't want garbage to set
'UML|New Project|unknown classifier|Create classifier' to 'No'

steps:
1. create new platform-independent uml project
2. add class diagram with name 'basics'
3. place two datatypes 'type1' and 'type2' to the diagram
4. add package with scoped class diagram to the project
5. add class 'myClass' to the diagram
6. invoke 'Inser Attribute' on the class
7. enter '- att : type1' attribute and finish edition
8. invoke 'Insert Operation' on the class
9. enter + op( ) : type2 and finish edition
notice: there are 'int' and 'void' datatypes in model
BUG: these elements are garbage in the model, they aren't used.
workaround: delete these element from project tree after model completed