remove unused import

Author: mantepse

src/sage/combinat/sf/witt.py

@@ -23,7 +23,6 @@
 from sage.arith.misc import divisors
 from sage.combinat.integer_lists.invlex import IntegerListsLex
 from sage.combinat.partitions import ZS1_iterator
-from sage.matrix.constructor import matrix
 from sage.misc.cachefunc import cached_method