python - fe: Remove unused attribute.

Log Message:
-----------
Remove unused attribute.

(Can't remember what I was going to use it for...)

Modified Files:
--------------
fe/src:
tracenull.py (r1.11 -> r1.12)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/src/tracenull.py.diff?r1=1.11&r2=1.12)