cleanup test_backend.py
cleanup test_backend.py

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