I have created some list of properties under the TestCase. For example look at the following screenshot.
Just for completeness:
Another quick but dirty and dangerous way is to modify the soapui-project.xml and remove the property nodes with a text editor.
Be aware that you can break your whole project if you do something wrong!
You should create a copy of your soapui-project.xml and do the following steps:
deleteMedeleteMe in your soapui-project.xml