Simplify dtype
Simplify dtype

hvy/chainer,tkerola/chainer,niboshi/chainer,chainer/chainer,hvy/chainer,wkentaro/chainer,okuta/chainer,keisuke-umezawa/chainer,okuta/chainer,okuta/chainer,niboshi/chainer,keisuke-umezawa/chainer,okuta/chainer,wkentaro/chainer,wkentaro/chainer,chainer/chainer,hvy/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,chainer/chainer,pfnet/chainer,wkentaro/chainer,hvy/chainer,chainer/chainer,niboshi/chainer,niboshi/chainer