Remove unused variable.

apachedex/__init__.py

@@ -262,7 +262,6 @@ class GenericSiteStats(object):
 
   def accumulate(self, match, url_match, date):
     self.apdex[date].accumulate(match)
-    duration = self.getDuration(match)
     if url_match is None:
       url = match.group('request')
     else: