Simplify backward of amax
Simplify backward of amax

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