If you justify the defects in the code, Polyspace automatically sets the review settings of the defect in the results accordingly. By setting the severity to "Not a defect" as you did in your example, the results should match that.
You mentioned, that the defects are still visible. Indeed it is not possible to delete the defect completely from the results, it is only possible to justify the defect. It will still be visible there, but with the severity, status and the comment of your justification in the code.
With that being said another common mistake is that the justification in the code is not in the same line as the defect. You could justify the same defect in multiple lines of code by using the syntax /* polyspace:begin and /* polyspace:end, as described here: Review Comments
Have a great day! ~Lucas