Remove unused import.
Remove unused import.

keisuke-umezawa/chainer,delta2323/chainer,tkerola/chainer,benob/chainer,benob/chainer,chainer/chainer,jnishi/chainer,chainer/chainer,rezoo/chainer,chainer/chainer,cupy/cupy,kikusu/chainer,cupy/cupy,chainer/chainer,niboshi/chainer,wkentaro/chainer,hvy/chainer,ktnyt/chainer,hvy/chainer,kiyukuta/chainer,hvy/chainer,ktnyt/chainer,cupy/cupy,ktnyt/chainer,jnishi/chainer,okuta/chainer,ronekko/chainer,jnishi/chainer,okuta/chainer,ktnyt/chainer,anaruse/chainer,jnishi/chainer,niboshi/chainer,cupy/cupy,niboshi/chainer,keisuke-umezawa/chainer,okuta/chainer,wkentaro/chainer,pfnet/chainer,ysekky/chainer,niboshi/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,kikusu/chainer,kashif/chainer,wkentaro/chainer,wkentaro/chainer,keisuke-umezawa/chainer,aonotas/chainer