Partially revert c12064cc0811e39e38129ae06dc74f4d1194be80
Partially revert c12064cc0811e39e38129ae06dc74f4d1194be80

avoid cupy.einsum

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