. at the end of the permissions is probably not relevant here. It indicates ACLs and/or SElinux attributes apply. See this question for more details.
If the user
ss cannot delete this directory it is probably because he does not have write permission on the parent dir of this backup dir.
Add write permission for user
ss to the parent directory of the directory backup to allow removal.
Deleting a file or directory requires write directory to the parent directory because that is the file you are editing.
If user ss has write permissions on the parent directory and you are still unable to remove the directory check acls (using
getfacl) and SELinux context (using