Remove unused import (struct.unpack)

Code was switched to using struct.Struct().unpack in 7fba4d2.

Author: antonv6

kaitaistruct.py

@@ -1,7 +1,6 @@
 import itertools
 import sys
 import struct
-from struct import unpack
 from io import BytesIO  # noqa
 
 PY2 = sys.version_info[0] == 2