Removed unnecessary dynamic cast
Removed unnecessary dynamic cast

wkentaro/chainer,niboshi/chainer,hvy/chainer,wkentaro/chainer,niboshi/chainer,chainer/chainer,hvy/chainer,hvy/chainer,chainer/chainer,chainer/chainer,niboshi/chainer,wkentaro/chainer,wkentaro/chainer,pfnet/chainer,niboshi/chainer,hvy/chainer,chainer/chainer