Trojans cannot be cleaned they are full of junk..so when Symantec tries to clean it first because first it looks at it as a good file..but when it finds out its full of junk..it will delete it
So it has cleaned it by deleting it... if the first option would have been to quarantine it would have directly sent it to quarantine rather than trying to clean it...
Trojans can not be cleaned as they are full of junk/Malicious codes.