I don't know if you are crazy or not but you are certainly still grieving. Since I believe that our spirit never dies and is always around the people we love I would be able to part with those shirts, perhaps you feel closer to Harry by hanging on to them but I'm sure there are times when you feel his presence around anyway. If you are happy to keep a few shirts then do so, it's what makes you feel good and not what anyone else thinks anyway.
RE: AM I CRAZY!!???
I don't know if you are crazy or not but you are certainly still grieving. Since I believe that our spirit never dies and is always around the people we love I would be able to part with those shirts, perhaps you feel closer to Harry by hanging on to them but I'm sure there are times when you feel his presence around anyway. If you are happy to keep a few shirts then do so, it's what makes you feel good and not what anyone else thinks anyway.