Removed unused import. (#292)

Update dupefilter.py

Author: sourcepirate

src/scrapy_redis/dupefilter.py

@@ -4,7 +4,6 @@
 import time
 
 from scrapy.dupefilters import BaseDupeFilter
-from scrapy.utils.request import request_fingerprint
 from scrapy.utils.python import to_unicode
 from w3lib.url import canonicalize_url