Remove unused import.

Lib/collections.py

@@ -12,7 +12,7 @@ import sys as _sys
 import heapq as _heapq
 from weakref import proxy as _proxy
 from itertools import repeat as _repeat, chain as _chain, starmap as _starmap, \
-                      ifilter as _ifilter, imap as _imap, izip as _izip
+                      ifilter as _ifilter, imap as _imap
 
 ################################################################################
 ### OrderedDict