Remove assert because static ndim indexer is used only in Release build, and assert is removed in Release build
Remove assert because static ndim indexer is used only in Release build, and assert is removed in Release build

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