Remove unused import.
Remove unused import.

jnishi/chainer,wkentaro/chainer,hvy/chainer,jnishi/chainer,ronekko/chainer,okuta/chainer,keisuke-umezawa/chainer,wkentaro/chainer,okuta/chainer,okuta/chainer,keisuke-umezawa/chainer,jnishi/chainer,ktnyt/chainer,ktnyt/chainer,niboshi/chainer,okuta/chainer,tkerola/chainer,hvy/chainer,keisuke-umezawa/chainer,niboshi/chainer,niboshi/chainer,hvy/chainer,ktnyt/chainer,chainer/chainer,chainer/chainer,keisuke-umezawa/chainer,chainer/chainer,pfnet/chainer,wkentaro/chainer,wkentaro/chainer,jnishi/chainer,chainer/chainer,aonotas/chainer,hvy/chainer,niboshi/chainer,anaruse/chainer,rezoo/chainer,ktnyt/chainer