Remove unnecessary imports

Author: bartvm

autograd/core.py

@@ -1,8 +1,6 @@
 from __future__ import absolute_import
 import sys
 import types
-import numpy as np
-import cupy as cp
 from functools import partial
 import warnings
 from .errors import defgrad_deprecated

autograd/util.py

@@ -4,7 +4,6 @@
 from builtins import range
 
 import autograd.numpy as np
-import autograd.cupy as cp
 from autograd.convenience_wrappers import grad
 from autograd.core import vspace, vspace_flatten, getval