hgweb: removed unnecessary del before function return

Deleting tmpl just before the return statement should have no effect
since tmpl goes out of scope anyway. But it confuses pyflakes who
thinks tmpl is undefined when it is used in the except blocks below.

mercurial/hgweb/hgweb_mod.py

@@ -168,7 +168,6 b' class hgweb(object):'
                 req.respond(HTTP_OK, ctype)
 
             req.write(content)
-            del tmpl
             return []
 
         except revlog.LookupError, err: